JP3171326B2 - Thick steel plate manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thick steel plate, and more particularly, to a method for producing a hot rolled high-temperature steel plate, which is cooled and then cut to a small amount. The present invention relates to a method for manufacturing a thick steel plate.

[0002]

2. Description of the Related Art Generally, a hot-rolled high-temperature steel sheet has a camber or an up-and-down warp in a plane when the steel sheet is cut due to uneven temperature and residual stress generated during manufacturing. Warpage occurs, that is, so-called straining distortion is likely to occur.

In recent years, as a method for producing a high-strength, high-toughness thick steel plate, so-called controlled rolling, in which rolling is performed in a specific temperature range, and accelerated cooling, in which a hot steel plate after rolling is strongly cooled, are generally performed. Have been done. As a method of accelerated cooling, a method is generally used in which cooling is performed by injecting cooling water from above and below while passing a steel sheet in a horizontal state online.
The temperature distribution in the sheet width direction of the steel sheet before the accelerated cooling is such that the heat is two-dimensionally radiated from the end of the sheet from the extraction of the slab in the heating furnace to the end of the rolling. Is lower than the temperature.

Therefore, when accelerated cooling is performed in this state, even if uniform cooling is performed in the width direction, the temperature distribution before cooling is inherited in a similar manner as it is, and the temperature at the end of the plate is maintained even after the cooling is completed. Is lower than the temperature at the center of the sheet width. When leveling (hot straightening) is performed in this state, even if the plate shape is flat at the end of leveling, the amount of heat shrinkage between the plate edge and the plate center is determined according to the temperature distribution existing in the width direction. A difference occurs, and when the temperature reaches room temperature, a compressive stress is generated at the center of the plate and a tensile stress is generated at the end of the plate. If this plate is cut as it is, the residual stress is released, and a cut distortion as shown in FIG. 5 occurs.

Means for eliminating the stripping distortion are as follows: (1) Recognizing the temperature drop amount and the temperature drop range around the central portion of the steel sheet in the rolling process, quantifying each, and water-cooling the upper and lower surfaces of the central portion. Method (JP-A-62-93)
(No. 010) (2) A method of eliminating temperature unevenness by cooling a high temperature part with water in order to flatten the temperature distribution in the width direction before accelerated cooling (Japanese Patent Application Laid-Open No. 60-36625). ) Method of performing cooling to flatten the temperature distribution in the width direction before accelerated cooling (Japanese Patent Laid-Open No. 60-36625) (4) A leveling roll is provided in an accelerated cooling device, and straightening is performed while cooling. Method (JP-A-61-231124)
(5) A method of reducing cooling at the end of a sheet during accelerated cooling so that the temperature distribution in the width direction of the steel sheet becomes flat after accelerated cooling (Japanese Patent Application Laid-Open Nos. 62-289315 and 55-15)
No. 3616, Utility Model Registration No. 2549694,
JP-A-58-32511, JP-A-6-28553
No. 1, JP-A-6-184623) has been proposed. Further, a so-called tempering treatment has been performed in which a heat treatment for removing strain is performed for the purpose of removing the stress remaining inside after accelerated cooling.

[0006]

However, in the rolling process disclosed in Japanese Patent Application Laid-Open No. 62-93010, the amount of temperature drop and the range of temperature drop around the center of the steel sheet are recognized, and each of them is quantified. In the method of water cooling the upper and lower surfaces of the central part, the temperature difference between the plate central part and the plate end part described in the same specification is accelerated cooling and in the air cooling process after straightening, and the critical temperature difference at which buckling of the steel sheet occurs below. If the critical temperature difference at which buckling occurs even if the center of the plate is cooled is large, for example, if the steel plate is thick, the material of the plate center and the plate end can be formed without buckling. There is a problem that a difference is inevitable.

Further, in the method disclosed in Japanese Patent Application Laid-Open No. 60-36625, in which cooling is performed so as to eliminate a high temperature portion in order to flatten the temperature distribution in the width direction before accelerated cooling, partial cooling is performed. Distortion occurs during the cooling process, and this distortion causes the cooling water flow in the width direction to be uneven in the next cooling in the accelerated cooling device, or the cooling water locally stays and causes another temperature unevenness. There is.

Further, in the method of cooling to flatten the temperature distribution in the width direction before the accelerated cooling, the method of straightening before and after the cooling, and the method of cooling to flatten the temperature distribution in the width direction are described. It is conceivable to perform straightening immediately, but in this method, the temperature at the end of the steel sheet further decreases with time during straightening, and before the accelerated cooling, the temperature distribution in the width direction of the steel sheet is again obtained. Thus, at the start of accelerated cooling, the temperature at the end of the plate is lower than that at the center of the plate, and there is a problem that the cooling effect of flattening the temperature distribution cannot be sufficiently obtained.

Further, a leveling roll is provided in a rapid cooling device as disclosed in JP-A-61-231124,
In the method of performing the correction while cooling, when the correction is performed in the accelerated cooling device, there is a problem that the presence of the leveling rolls obstructs the flow of the cooling water and promotes local cooling unevenness. Further, at the end of cooling, the steel sheet surface temperature is in a state of being lowered, but a short time after leaving the cooling device, the steel sheet surface temperature rises due to reheating. When the temperature of the upper surface and the lower surface of the steel sheet are different in the recuperation stage (for example, due to a minute imbalance in cooling of the upper and lower surfaces during accelerated cooling), there is a problem that a very large warpage distortion occurs. .

[0010] A method of reducing the cooling at the end of the plate during accelerated cooling so that the temperature distribution in the width direction of the steel sheet becomes flat after the accelerated cooling, that is, the amount of cooling water supplied to the center of the laminar cooling water is reduced. A method of reducing the cooling of the plate edge by reducing the amount of cooling water supplied to the plate edge (Japanese Patent Application Laid-Open Nos. 62-289315 and 55
No. 153616), a method of cutting off cooling water that falls to the end by a shielding plate (utility model registration 25496)
No. 94, JP-A-58-32511), in a slit nozzle for injecting cooling water from a slit nozzle along a plate, a shield movable in the width direction for shielding a slit at a slit portion at a tip end of the slit nozzle. To prevent cooling water from splashing on the edge of the plate (JP-A-6-285531, JP-A-6-184623)
For both of these methods, during accelerated cooling,
The cooling start temperature at the end of the plate is lower than the cooling start temperature at the center of the plate, and as a result, the strength and toughness of the end of the plate differ from those in the center of the plate, causing variations in product quality. However, there is a problem that it does not meet the conditions of recent controlled rolling and controlled cooling which require strict temperature control.

Further, since the amount of cooling water to the plate end is smaller than the amount of cooling water at the center of the plate, the cooling speed at the plate end becomes smaller than the cooling speed at the center of the plate. There is a problem that a cooling rate cannot be obtained, which causes a variation in product quality as well as a variation in a cooling start temperature in a width direction.

When residual stress remains after accelerated cooling, a stress relief annealing process is generally performed to remove the stress. However, this requires enormous energy and time for reheating. , Which is disadvantageous in terms of cost.

[0013] The present invention has been made in view of such circumstances, and even if the cutting is performed while cooling, the stripping distortion is small, and a steel sheet of a uniform material can be stably online on the entire steel sheet. An object is to provide a method that can be manufactured.

[0014]

An object of the present invention is to provide a method of manufacturing a steel sheet by manufacturing a steel sheet by accelerating and cooling a hot-rolled high-temperature steel sheet, wherein a cooling device provided between a rough rolling mill and a finishing mill is provided. In order to compensate for the temperature drop near the plate edge generated from the heating furnace to the end of rough rolling, and the temperature drop near the plate edge estimated to occur during finish rolling, the temperature in the sheet width direction is compensated. Cooling with distribution, after finish rolling,
The problem is solved by a method for manufacturing a thick steel plate, wherein accelerated cooling is performed under uniform cooling conditions in the width direction.

At the end of the rough rolling, by performing cooling with a temperature distribution in the width direction of the sheet, the amount of temperature drop at the sheet edge accumulated up to that point and the sheet edge estimated to be generated during finish rolling after that. By compensating for the temperature drop of the portion, the temperature distribution in the width direction of the steel sheet before the accelerated cooling becomes flat. Further, even if the coarse steel plate is deformed by this cooling, it can be flattened by finish rolling.

Thereafter, when uniform cooling is performed in the width direction in the accelerated cooling device, the cooling speed and temperature history (cooling start temperature, cooling stop temperature) of each part of the steel sheet become constant in each part of the steel sheet, and a uniform material can be obtained. . Thereafter, even when hot straightening is performed, since the temperature is substantially uniform in the width direction of the sheet, no residual stress remains in the steel sheet after natural cooling, and thus no distortion occurs even when the strip is cut.

Further, in order to carry out the present invention, it is possible to use a cooling device for adjusting the temperature between the rough rolling and the finish rolling, which has been conventionally used in the controlled rolling, as it is, and a new cooling system can be used. No installation of equipment is required.

[0018]

(Embodiment 1) Next, the present invention will be described in detail with reference to embodiments. The first embodiment has a thickness of 250 mm, a width of 2000 mm,
A steel plate with a width of 4000 mm, a thickness of 25 mm and a product length of about 20 m is manufactured from a 3500 mm long slab by controlled rolling.

FIG. 1 shows the configuration of the equipment used in this embodiment. In FIG. 1, 1 is a rough rolling mill, 2 is a shower cooling device, 3 is a finishing rolling machine, 4 is a first hot straightening machine, 5 is an accelerated cooling device, 6 is a second hot straightening machine, and 7 is A cooling floor, 8 a surface thermometer after the rough rolling mill, 9 a surface thermometer for measuring a cooling start temperature, 10 a surface thermometer for measuring a cooling end temperature,
A surface thermometer 11 measures the temperature of the steel sheet after the correction.
The first hot straightening machine 4 corrects a shape defect caused by rolling in order to prevent uneven cooling during cooling, and the second hot straightening machine 6 is formed by accelerated cooling. This is to remove the distortion.

In this steel plate manufacturing facility, about 12
After descaling the slab heated to 50 ° C, the rough rolling mill 1
At a width of 4000 mm and a thickness of 65 mm. At this time, the number of passes of the rough rolling was 14 and the surface temperature of the steel sheet 9 at the end of the rough rolling was measured by the radiation thermometer 8. As a result, as shown in FIG. , The temperature near the center of the board is 1045 ℃
Met. That is, at this stage, the temperature at the plate edge was about 75 ° C. lower than that at the center of the plate, and the portion at which the temperature dropped reached a range of about 150 mm from the plate edge.

The shower cooling device 2 is a cooling device in which a number of spray cooling nozzles are arranged on the upper and lower surfaces of a steel plate over a length of 40 m. Commercial spray nozzles are staggered at a pitch of 100 mm in the width direction and 150 mm in the longitudinal direction. The upper nozzle is disposed 1.5 m above the transfer table, and the lower nozzle is disposed 300 mm below the transfer table.

In order to control the cooling capacity of the plate end, a plate for masking is inserted between the nozzle and the steel plate at the plate end on the lower surface. In this example, a masking plate was inserted from the end of the plate to 100 mm. In addition, on the upper surface, air was sprayed from the side of the line to the plate edge in a range of about 100 mm from the side of the line so that the cooling water did not splash on the plate edge, and was sprayed and dropped near the plate edge on the upper surface of the steel plate. The device is designed so that the cooling water does not touch the edge of the plate.

In this shower cooling device, the cooling capacity in the plate width direction, particularly the cooling capacity near the plate edge, can be changed by the above-described device configuration. Cooling capacity adjustment
For the lower surface, the amount of temperature adjustment and its width are determined by the length in the length direction of the steel plate into which the masking plate is inserted and the insertion depth (width), and for the upper surface, the number of nozzles in the length direction of the air jet nozzle. It is possible to change the temperature adjustment amount and its width depending on the position in the width direction.

The amount of temperature adjustment at the edge of the plate was determined as follows. The controlled rolling conditions for this sheet required that the finish rolling of a sheet thickness of 65 mm to 25 mm be performed in a temperature range of 850 ° C. to 900 ° C. or less. Therefore, it is necessary to lower the temperature around the center of the plate from 1045 ° C to 900 ° C or less, and the temperature at the plate edge from 970 ° C to 900 ° C or less, that is, at least 145 ° C and 70 ° C respectively.

For the central part of the plate, by using the cooling water amount which is the maximum cooling capacity of the shower cooling device,
The temperature can be lowered by 145 ° C in about 30 seconds. At this time, from the heating furnace extraction to the end of rough rolling, the sheet edge was cooled by 75 ° C compared to the center of the sheet. Since it was cooled, it was necessary to cool and adjust the plate edge in total at about 90 ° C.

Therefore, the masking length and depth of the lower surface, the number of nozzles of the air to be injected on the upper surface in the length direction of the steel plate, and the injection position thereof are determined so that such cooling adjustment is possible. At this time, the amount of temperature drop at the end of the plate during the finish rolling can be estimated and determined by a two-dimensional heat transfer calculation inside the steel plate.

FIG. 2B shows a temperature distribution in a stage after the temperature is adjusted by the shower cooling device 2. Since the cooling adjustment width of the plate edge in this cooling is equivalent to the temperature drop near the plate edge generated from the heating furnace to the end of finish rolling,
Approximately 1.5 times the slab thickness at the maximum from the plate edge, usually about the width of the slab thickness, even in this embodiment at most 25
It is about 0 mm. Actually, it differs depending on the rolling conditions (the number of passes and the number of tentative rolling (the number of times the slab is rotated by 90 degrees and rolled)).

In this embodiment, since the number of passes from the slab to the plate thickness (65 mm) is relatively small,
The actual temperature adjustment width was 150 mm from the edge of the plate. In this cooling, cooling conditions are determined so that each part of the steel sheet does not undergo transformation due to overcooling, that is, so that the temperature in finish rolling does not become lower than the Ar ₃ transformation point.

Subsequently, this steel sheet was rolled by a finishing mill 3 to 25 mm. When the temperature distribution on the exit side of the finishing mill 3 was measured by the surface thermometer 8, the temperature deviation in the plate was about 10 ° C. as shown in FIG.

The steel sheet was immediately conveyed to the first hot straightening machine 4 and subjected to leveling. This first hot straightening machine 4 is a straightening machine composed of five rolls having a roll diameter of 450 mm.
In the last three rolls, the amount of C warpage in the plate width direction is intentionally generated by adjusting the pushing amount of the upper roll. Note that the amount of C warpage in the sheet width direction changes depending on the amount of indentation, and depending on the amount of indentation, a downwardly convex or upwardly convex C-warp is generated.
%, And leveling was performed with the amount of depression.

The steel sheet leveled by the first hot straightening machine 4 is sent to an acceleration cooling device 5 where it is cooled. FIG. 3 shows a schematic diagram of this accelerated cooling device. In the following figures, the same elements as those shown in the preceding figures are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 3, 12 is an upper roll, 13
Is a lower roll, 14 is a slit nozzle, and 15 is a circular nozzle.

The accelerated cooling device 5 cools the steel plate immediately after rolling online while transporting the steel plate between 20 pairs of upper rolls 12 and lower rolls 13 (see FIG. 1).
0 sets), and the pitch between the rolls is 1000 mm. In these 20 sets of restraining rolls, the lower roll 13 also serves as a transport roll and is of a fixed type, but the upper roll 12 has a diameter of 0.25 m and can be moved up and down with a gap of 0.5.
It can be controlled at mm pitch. Further roll 12 on this
When a steel sheet having a thickness greater than the set gap passes when the steel sheet passes, a restraining force is applied to the steel sheet via hydraulic cylinders from both ends of the upper roll.

On the upper surface side between the upper rolls 12, from the upper roll 12 on the upstream side in the sheet transport direction to the upper roll 12 on the downstream side, the slit nozzle 14 sends 2 m per 1 m in the sheet width direction in the sheet traveling direction. ³ / min of water is flowing along the plate. On the other hand, on the lower surface side, it is provided at a pitch of 100 mm,
Water is jetted from a circular tube nozzle 15 submerged in water, and cooling is performed by a liquid flow generated by the accompanying flow. Here, uniform cooling was performed in the width direction.

At this time, the temperature distribution of the steel sheet was
When measured at 0, at the start of cooling, 785
° C, 775 ° C at the edge of the plate, 5% at the center of the plate at the end of cooling
00 ° C, 485 ° C at plate edge, cooling rate is almost 30 ° C / s
Was almost uniform throughout the plate.

The steel plate cooled by the cooling device is then
Was sent to the hot straightening machine 6 to correct the warpage generated during cooling. The second hot straightening machine 6 is a hot straightening machine having nine rolls. After the straightening, the steel sheet did not have any significant warpage or deformation, and the temperature distribution after the straightening was measured by the surface thermometer 15, and the temperature deviation in the sheet was within 10 ° C.

Further, the steel sheet was conveyed to the cooling floor 7 and allowed to cool naturally. Since there was no particularly large deformation after cooling in the cooling floor 7, the product was obtained without any special refining work. Further, as a result of examining the material of the steel sheet obtained after cooling, there was little variation in hardness and strength in the width direction, and there was no particularly large difference in hardness distribution. The variation in strength was 5 MPa or less in yield stress, and an extremely homogeneous steel plate was obtained.

Thereafter, gas cutting was performed in eight pieces with a width of 500 mm in the width direction. When the camber amount of the strip material was measured after the stripping, it was 5 mm or less per 10 m, and the stripping hardly deformed. Therefore,
A step of removing residual stress such as stress relief annealing was unnecessary.

In this embodiment, the temperature compensation of the plate end is performed at the time of adjusting the temperature between the rough rolling in the rough rolling mill and the finish rolling in the finishing rolling mill. In the case of performing finish rolling, the effect of the present invention can be obtained by adjusting the temperature in the middle. Further, when the rough rolling and the finish rolling are divided into a plurality and the temperature adjustment is performed a plurality of times in the middle, the temperature adjustment in the width direction is performed a plurality of times before the accelerated cooling so that the temperature distribution in the sheet width direction becomes flat. The adjustment may be made separately.

In this embodiment, the cooling device for adjusting the temperature is performed in a cooling device separate from the rolling mill. However, the same temperature adjustment can be performed to some extent by a cooling device attached to the rolling mill. However, in order to realize the conditions of the controlled rolling, for example, when performing rolling such that the rolling reduction is obtained at a certain temperature or less, it is preferable to perform the temperature control with a cooling device independent of the rolling mill, because the temperature controllability is good. .

(Embodiment 2) Next, a second embodiment of the present invention will be described. In this example, the thickness is 250 m by hot rolling.
m, width 1400mm, length 3000mm slab width 3000mm, thickness 18m
A thick steel plate having a product length of about 20 m was manufactured by controlled rolling, and the equipment used was the same as that used in Example 1, as shown in FIGS. 1 and 3. However, in this embodiment, the first hot straightening machine 4 is not used.

In this steel plate manufacturing facility, about 12
After descaling the slab heated to 50 ° C, the rough rolling mill 1
At a width of 3000 mm and a thickness of 50 mm. At this time, the number of passes of the rough rolling was 16 passes, and the surface temperature of the steel sheet at the end of the rough rolling was measured by the radiation thermometer 8, and as shown in FIG. ℃, the temperature near the center of the plate is about 1
025 ° C. That is, at this stage, the temperature of the plate edge was lower by about 95 ° C. than that of the center of the plate, and the portion where the temperature dropped reached a range of about 140 mm from the plate edge.

In the shower cooling device 2, in order to control the cooling capacity of the plate edge, the lower surface is 110 m from the plate edge.
A masking plate was inserted between the nozzle and the steel plate up to m. On the upper surface, air is sprayed from the side of the line to the plate edge in a range of 110 mm from the side of the line so that the cooling water does not splash on the plate edge. The edge of the plate was not touched.

The temperature adjustment amount at the end of the plate was set such that the end of the plate was supercooled by 95 ° C. compared to the center of the plate from the extraction of the heating furnace to the end of the rough rolling. It was presumed to be overcooled by about 15 ° C. Therefore, it was necessary to adjust the cooling of the plate edge by about 110 ° C. in total. Therefore, based on this, the masking length and depth of the lower surface, the number of nozzles of air to be injected on the upper surface, and the injection position thereof were determined. FIG. 4B shows a temperature distribution in a stage after the temperature adjustment is performed by the shower cooling device 2.

Subsequently, this steel sheet was rolled to 18 mm by a finishing mill 3. The temperature distribution on the exit side of the finishing mill 3 is shown in FIG.
As shown in the figure, the temperature was kept at about 10 ° C. in the whole plate.

This steel sheet was sent to the accelerating cooling device 5 and cooled. At this time, the cooling start temperature of the steel
When measured at 3, it was 785 ° C at the center of the plate and 775 ° C at the end of the plate, and when the cooling end temperature was measured by the surface thermometer 10, it was 500 ° C at the center of the plate and 485 ° C at the end of the plate. The cooling rate was almost uniform at 30 ° C./s inside the plate.

The steel sheet cooled by the accelerated cooling device 5 was subsequently sent to a second hot straightening machine 6, where the warpage generated during cooling was corrected. After straightening, there is no significant warpage or deformation of the steel sheet,
Further, as measured by the surface thermometer 11, the temperature deviation in the plate after the correction was within 10 ° C.

Further, the steel sheet was conveyed to the cooling floor 7 and allowed to cool naturally. Even after cooling with the cooling floor 7, there is no particularly large deformation,
Therefore, the product was obtained without any special refining work.
Further, as a result of examining the material of the steel sheet obtained after cooling, there was little variation in hardness and strength in the width direction, and there was no particularly large difference in hardness distribution. The variation in strength is 5MPa in yield stress
A very homogeneous steel plate with the following was obtained.

Thereafter, the strip was cut by gas cutting into eight strips with a width of 500 mm in the width direction. When the camber amount of the strip material was measured after the stripping, it was 5 mm or less per 10 m, and the stripping was hardly deformed. Therefore,
A step of removing residual stress such as stress relief annealing was unnecessary.

Comparative Example As a comparative example, a steel sheet having the same size as that of Example 1 was manufactured under four kinds of unusual operating conditions. That is, a thick steel plate having a width of 4000 mm, a thickness of 25 mm and a product length of about 14 m was manufactured from a slab having a thickness of 250 mm, a width of 1600 mm and a length of 3500 mm. In each of the comparative examples, the cooling in the width direction is not performed by the shower cooling device 2 and uniform cooling (cooling water amount is constant in the width direction) is performed.

(Comparative Example 1) The shower cooling device 2 is a method in which uniform cooling is performed in the width direction and cooling is performed in order to flatten the temperature distribution in the width direction before accelerated cooling by the accelerated cooling device 5. . That is, rough rolling → shower cooling (widthwise uniform cooling) → finishing rolling → plate edge adjustment cooling → accelerated cooling (widthwise uniform cooling) → straightening by the second hot straightening machine → cooling on the cooling floor, The steel plate was manufactured by the process described above.

In this method, the hot steel sheet after rolling was cooled in order to flatten the temperature distribution in the width direction. As a result, the edge of the sheet was warped 30 mm higher than the center of the sheet after cooling. In this case, a convex cooling distortion occurred under the so-called C warpage.

At this stage, the temperature distribution in the width direction was almost flat and the temperature deviation was ± 10 ° C., but in the finish rolling stage, the temperature distribution was provided in the width direction (the plate edge portion was compared to the plate center portion compared to the center portion). It is considered that the strain accumulated from that stage became apparent due to the flat shape finished at a temperature of about 50 ° C is low).

The acceleration cooling device 5 aimed at uniform cooling in the width direction, but this distortion caused the cooling water flow in the width direction to be non-uniform in the cooling in the acceleration cooling device 5, and the center at the stage when the cooling water passed through the acceleration cooling device 5. Cooling water stayed locally near the part, causing uneven cooling. The temperature difference in the width direction of the steel sheet after the completion of the accelerated cooling was about 70 ° C.

After that, the warpage was corrected by a hot straightening machine. After cooling, the camber amount of the strip was 90% per 10 m.
It was greatly deformed to mm. Therefore, this material cannot eliminate the camber even in a process of removing residual strain such as stress relief annealing. The variation in the tensile strength in the plate was 40 MPa because of the variation in the temperature at which the plate was accelerated to stop cooling.

(Comparative Example 2) The shower cooling device 2 is a method in which uniform cooling is performed in the width direction, a leveling roll is provided in the acceleration cooling device 5, and correction is performed while accelerating cooling. In other words, rough rolling → shower cooling (widthwise uniform cooling) → finishing rolling → straightening during accelerated cooling (widthwise uniform cooling)
A steel sheet was manufactured through the steps of: → straightening by a second hot straightening machine → cooling on a cooling floor.

In this method, the plate was flat at the end of the accelerated cooling, but after leaving the accelerated cooling device 5 for a while, the end of the plate was moved to the center in response to the steel plate surface temperature recovering. A large C-warp, which is 50 mm higher than the part and convex downward, occurred.

After that, the warpage was corrected by a hot straightening machine. After cooling, the camber amount of the strip was 80% per 10 m.
It was greatly deformed to mm. Therefore, this material could not eliminate the camber even in the step of removing residual strain such as stress relief annealing. The variation in the tensile strength in the plate was 10 MPa.

(Comparative Example 3) A method different from Example 1 only in that uniform cooling in the width direction is performed by the shower cooling device 2. In other words, rough rolling → shower cooling (uniform cooling in the width direction) → finishing rolling → straightening by the first hot straightening machine → plate edge adjustment cooling → accelerated cooling (uniform cooling in the width direction)
→ Steel plate is manufactured by a process of straightening by a second hot straightening machine → cooling in a cooling floor.

In this method, the temperature difference in the width direction of the steel sheet before and after the accelerated cooling was about 80 ° C. The sheet was straightened by the hot straightening machine and straightened into a flat plate, but a convex C warpage occurred during cooling on the cooling floor. After that, stripping was performed and the camber amount of the stripped material was examined. It was greatly deformed to 65mm per 10m. Therefore, this material required a step of removing residual strain such as stress relief annealing. The variation in the tensile strength in the plate was 30 MPa. This is presumably because at the start of the accelerated cooling, the temperature in the plate varied greatly, and was about 70 ° C.

(Comparative Example 4) The same manufacturing process was performed in the same equipment configuration as in the example, except that the shower cooling device 2 uniformly cooled in the width direction. In this method, the cooling capacity of the cooling water at the plate edge is adjusted by inserting a shielding body at the nozzle outlet for the upper surface and inserting a masking plate for the lower surface. That is, it is a method of compensating for the temperature drop at the end of the plate in the accelerated cooling device.
Shower cooling (uniform cooling in the width direction) → finishing rolling → straightening by the first hot straightening machine → accelerated cooling (plate edge cooling control) → straightening by the second hot straightening machine → cooling process on the cooling floor Produced a steel sheet.

In this method, the temperature difference in the width direction of the steel sheet before the accelerated cooling is about 75 ° C., but the temperature distribution in the sheet width direction after the accelerated cooling is almost the same as that of the embodiment, and the difference is about 15 ° C. Met. As a result, the camber amount of strips is 10 per 10m.
mm.

As a result of examining the material of the steel sheet obtained after cooling, there was a large variation in hardness and strength in the width direction, and in particular, there was a variation in strength and hardness at the plate edge. Strength YS for the entire board
The difference greatly varied to 50 MPa. This is because the temperature at the edge of the plate on the entrance side of the accelerated cooling device is lower than that at the center of the plate. This is probably because the cooling rate could not be obtained.

Table 1 shows the results of the examples and the comparative examples.

[0064]

[Table 1]

[0065]

As is clear from the above description, according to the present invention, the following effects can be obtained. (1) According to the present invention, it is possible to manufacture a steel sheet with less variation in strength of the entire steel sheet and less stripping distortion. (2) The end of the plate is not out of specification due to overcooling or insufficient cooling of the end of the plate, and the product yield is improved. (4) The deformation of the plate is reduced, the refining process by a leveler or a press can be omitted, and the manufacturing cost can be reduced. (5) The plate after cooling can be cut without performing strain removal by stress relief annealing or the like. Therefore, energy for reheating is omitted, and the process can be saved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of equipment used in an embodiment of the present invention.

FIG. 2 is a diagram showing a temperature distribution in a steel sheet in one example of the present invention.

FIG. 3 is a diagram showing an outline of an accelerated cooling device used in an embodiment of the present invention.

FIG. 4 is a diagram showing a temperature distribution in a steel sheet according to another embodiment of the present invention.

FIG. 5 is a diagram schematically showing distortion (camber) generated at the time of cutting.

[Explanation of symbols]

 1-Rough rolling mill 2-Shower cooling device 3-Finish rolling mill 4-Hot straightening machine 5-Accelerated cooling device 6-Hot straightening machine 7-Cooling floor 8-Surface thermometer after rough rolling mill 9-Cooling start Surface thermometer for measuring temperature 10-Surface thermometer for measuring cooling end temperature 11-Surface thermometer for measuring the temperature of steel sheet after straightening 12-Upper roll 13-Lower roll 14-Slit nozzle 15-Circular nozzle

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shogo Tomita 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Masahisa Fujikake 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (72) Inventor Shunichi Sugiyama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-63-63520 (JP, A) JP-A-60-36625 ( JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B21B 45/02 320

Claims (1)

(57) [Claims] 1. A method for manufacturing a steel sheet by manufacturing a steel sheet by accelerating and cooling a hot-rolled high-temperature steel sheet, wherein a cooling device provided between a rough rolling mill and a finishing mill completes rough rolling from a heating furnace. Cooling with a temperature distribution in the sheet width direction is performed so as to compensate for the amount of temperature drop near the sheet edge that has occurred up to and the amount of temperature drop near the sheet end that is estimated to occur during finish rolling, A method for producing a thick steel plate, comprising: after finish rolling, performing accelerated cooling under uniform cooling conditions in the width direction.