JP2610019B2 - Cooling method of hot steel plate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a forced cooling method for obtaining a good shape and uniform material such as a hot steel plate, particularly a hot-rolled thick steel plate.

(Prior art) In recent thick plate manufacturing processes, so-called temper cooling, which combines heating condition control and forced cooling immediately after controlled rolling for the purpose of reducing alloy elements, saving heat treatment, and developing new steel types. Process research is active,
Various tempering cooling facilities have already been commercialized at steel companies.

These series of controls, from heating to cooling, are aimed at controlling the transformation composition of steel plates and improving mechanical properties.However, heating and rolling control technology has been elucidated by metallurgical mechanisms through years of research. While it has been established as an on-line manufacturing technology, the forced cooling technology, although its metallurgical mechanism has been elucidated, is still inadequate in terms of cooling control technology, especially shape control technology.

That is, the forced cooling of the hot steel sheet is performed by injecting cooling water onto the upper and lower surfaces of the hot steel sheet from a group of nozzles arranged on the upper and lower surfaces of the hot steel sheet on the rear surface of the rolling mill or the hot steel straightening machine on the hot steel sheet passing line. At this time, if cooling water is sprayed uniformly in the plate width direction, the temperature at the plate side end is lower than the center of the plate width at the start of cooling. It is known that the cooling rate is higher than that of the part, and a temperature difference occurs in the width direction of the plate, thereby significantly impairing the plate shape.

As a method for solving such a problem, Japanese Patent Laid-Open No. Sho 60-174833 discloses a method of shutting off cooling water at a plate edge. The cooling method is that the temperature at the end of the steel sheet is lower than the center by air cooling during rolling and transportation to the forced cooling device immediately before the start of cooling, and the steel sheet already has a temperature deviation in the sheet width direction. Since this temperature deviation is further increased, the temperature deviation is increased by blocking the cooling water in a predetermined area at the end of the steel plate to prevent the cooling of the end of the steel plate, and during the cooling or at the time of completion of cooling, the temperature in the width direction of the steel plate. And to obtain a steel plate having a good shape and a uniform material.

(Problems to be Solved by the Invention) According to the cooling method of the prior art described above, since the cooling water at the end of the steel plate is turned on and off in nozzle units, as shown in FIG. The temperature deviation tendency at the time of completion of cooling of the steel sheet edge at the time of cooling is different from the temperature recovery tendency after the completion of cooling with the shielding function, and the temperature recovery at the boundary between the steel sheet edge and the center is insufficient. A temperature drop occurs.
When the temperature drop at the boundary occurs, even if there is no temperature difference between the center and the end of the sheet width, the shape of the steel sheet after the forced cooling is deteriorated, and the shape of the steel sheet tends to become an ear wave shape.

However, even if there is a temperature drop at the boundary, if the value is small (for example, ΔT ≦ 30 ° C.), the steel sheet shape after cooling is good, but it is used by dividing it into slits in the sheet width direction when cutting a product. In such a case, warping or bending occurs after cutting, and correction is required. This temperature drop at the boundary is particularly likely to occur when the cooling completion temperature (average thickness) is 500 ° C or less.
It hardly occurs above 50 ° C.

FIG. 12A shows another problem of the conventional cooling method. The longitudinal direction of the cooling device is divided into three zones, and the closing length (indicated by the distance 1 from the steel plate side end) of each zone is indicated by oblique lines in the figure. The shielding length l is small. In such a shielding method, since the cooling shielding part at the end of the steel plate is on one straight line for each cooling zone, the difference between the cooling ability of the cooling shielding part and the cooling ability of the non-shielding part is too large. The temperature pattern becomes step-like. In a steel sheet having such a temperature pattern generated during cooling, even when the temperature at the time of cooling stop is uniform, a wave and a warp are easily generated at the end of the steel sheet.

As a method for solving this, for example, the above-mentioned Japanese Patent Application Laid-Open No.
No. 4833 discloses a shielding method as shown in FIG. 12 (b). That is, a method has been proposed in which the number of closed nozzles in the upper, lower, and sheet passing directions of the steel plate is increased or decreased in the longitudinal direction of the cooling device. However, this method allows a certain degree of correction only when the forced cooling device is sufficiently long and the number of blocking devices is large, but it requires equipment cost and prevents wave and warpage at the end of the steel plate. incomplete.

As described above, the conventional cooling control method in the width direction of the plate has considerably improved the cooling shape, but still has a problem.

(Means for Solving the Problems) In view of the problems of the conventional technology, the present invention focuses on the temperature pattern in the width direction of the steel sheet during the water cooling process, particularly, on the temperature pattern at the end of the steel sheet. The purpose is to increase or decrease the amount of cooling water in the vicinity of the end of the steel sheet in nozzle units so that it can be cooled within the temperature deviation of the steel sheet, and to manufacture a steel sheet having a good shape. While passing the hot steel sheet in the longitudinal direction above, it passes through a plurality of cooling zones, and a number of hot steel sheets are arranged in the cooling zone so as to be directed to the plate surface along the upper and lower width directions and the longitudinal direction of the hot steel sheet. The cooling method of spraying cooling water onto the steel sheet from the nozzles described above to cool the steel sheet at the center of the sheet width based on the actual measured value of the representative temperature of the steel sheet at the cooling zone entrance side and a predetermined cooling rate and cooling completion temperature. The cooling condition at the center of the steel sheet and the temperature change from the start of cooling at the center of the sheet width are calculated and determined. The temperature change from the start of cooling in the vicinity of the plate width side end is calculated based on the flow rate control pattern, and the temperature change from the start of cooling in the center of the plate width and the start of cooling in the vicinity of the plate width side end corresponding thereto. The width direction nozzle flow control pattern is determined such that the absolute amount of the temperature difference is equal to or less than the target value by comparing the temperature changes of the nozzles in the cooling zone according to the determined width direction nozzle flow control pattern. A method for cooling a hot steel sheet, wherein the flow rate is individually controlled. It is.

(Operation) As shown in FIG. 4, the relationship between the plate thickness and the cooling rate is such that when the plate thickness is increased, the cooling rate is rapidly reduced, and the cooling rate is reduced as the water density is reduced.

As shown in FIG. 5, the relationship between the plate width and the water injection pattern in the plate width direction is as shown in FIG. 5, since a material having a large plate width tends to have a large temperature drop region at the plate side end at the start of cooling. Since the area is increased and the material having a small width of the plate tends to have a small temperature drop region at the end on the side of the plate, there is no need to provide a region where the water injection amount is zero.

FIG. 6 (a) shows the relationship between the supercooling of the plate side end and the cooling rate.
FIG. 6 (b) shows the relationship between the supercooling of the plate side end and the cooling completion temperature. 6 (a), the higher the cooling rate,
It is clear from FIG. 6 (b) that the supercooling at the plate-side end becomes large, and that the higher the cooling completion temperature, the smaller the supercooling at the plate-side end.

Therefore, to prevent overcooling of the plate side end, the plate thickness,
In accordance with the plate width, the cooling start temperature, the cooling rate, and the cooling completion temperature, the area where the nozzle water injection amount is zero is increased / decreased, and the water injection amount is increased / decreased for each nozzle in order to prevent the water injection amount pattern from becoming stepwise. .

(Example) Next, the present invention will be described in detail based on an illustrated example. FIG. 1 is an overall configuration diagram of a cooling device showing one embodiment of the present invention.

After hot rolling, the hot steel sheet 1 is cooled to a predetermined temperature by a cooling device 10 under predetermined cooling conditions according to the material and dimensions. Reference numeral 2 denotes a transport roll for the hot steel sheet 1, and reference numeral 3 denotes a constraining roll which is disposed vertically above and below the transport roll 2, and is disposed so as to be able to move up and down by an elevating device (not shown). Only inside, it descends to the position that restrains the hot steel sheet.

The cooling water for cooling the hot steel plate is supplied by the water supply header 7,
The water is supplied to the spray device 4 through the water supply pipe 6 and the water amount control valve 5. In addition, the water amount control valve 5 controls the cooling water supplied through the water supply pipe 6 to a predetermined water amount for each cooling control zone, and supplies the water to the spray device of each cooling control zone.

A plurality of inlet thermometers 8 are arranged on the inlet side of the cooling device 10 in the plate width direction, detect the temperature in the plate width direction before the cooling of the hot steel plate 1 is started, and input the detected temperature to the inlet-side temperature calculator 11. The entry-side temperature calculation device 11 calculates the temperature distribution in the plate width direction before the start of cooling.

Further, a plurality of outlet thermometers 9 are arranged on the outlet side of the cooling device 10 in the sheet width direction to detect the temperature in the sheet width direction after the cooling of the hot steel sheet 1 is completed (after recuperation), and the outlet side temperature is measured. The temperature is input to the arithmetic unit 13, and the outlet-side temperature arithmetic unit 13 calculates the temperature distribution in the sheet width direction after the cooling is completed.

Numeral 12 is a cooling operation / control device for controlling the cooling device.The cooling operation / control device is provided based on operating conditions such as the steel type of the material to be cooled, dimensions, a target cooling start temperature, a cooling speed, and a cooling completion temperature given from the host computer 14. Calculate the cooling water amount and the passing speed of the control zone, and further control the cooling condition of the cooling device based on the temperature before the cooling start of the hot steel sheet to be cooled and the temperature of the cooling completion of the pre-coolant of the temperature calculating devices 11 and 13. In addition to the correction calculation, the nozzle flow control conditions around the steel plate side end of the spray device are calculated, and each component of the cooling device 10 is controlled.

In addition, as cooling control means for obtaining a good steel sheet shape, cooling control of the upper and lower surfaces of the steel sheet and cooling control of the front and rear end portions of the steel sheet are also important. These cooling controls are performed by a known method. Also, a method of calculating the temperature pattern in the sheet width direction from the temperature measurement result at the start of cooling, a method of calculating the amount of temperature drop per unit time from the cooling condition, and a steel sheet edge for equalizing the amount of temperature drop in the sheet width direction The method of calculating the amount of cooling water of the nozzle in the vicinity of the portion is also a known method.

Reference numeral 15 denotes a rotation speed detector that detects the rotation speed of the transport roll 2, and is connected to the cooling operation / control device 12.

Since the required amount of cooling water for each cooling control zone changes depending on the flow rate control amount of each nozzle of the spray device 4, the required flow rate control amount of each nozzle of the spray device is fed back to provide the required cooling amount for each cooling control zone. Control the amount of water.

Next, the configuration of the spray device 4 will be described. FIG. 2,
FIG. 3 shows a mechanism of controlling the nozzle flow rate near the steel plate side end. The nozzle flow rate control mechanism includes a nozzle header 21, a nozzle 25, a valve element 22 for controlling the amount of jetted water for each nozzle, a lever 23 connected to the rotary shaft of the valve element, a nozzle branch pipe 24 connecting each valve element to the nozzle, a lever Actuating a striker block 28 to set the opening of the valve body, a screw shaft 27 for moving the striker block and controlling the rotation angle of the lever, a screw shaft bearing 26, a driving device 29 for rotating the screw shaft and A rotation detector that detects the rotation speed of the screw shaft and the position of the striker block
29a, which controls the nozzle flow rate at the steel plate side end to a predetermined value for each spray device.

Further, as shown in FIG. 3, the nozzle flow control valve element 22 is
A water passage for the nozzle 25 is continuously formed on the nozzle header 21, and the lever 23 is moved in the rotating direction by the striker block 28 to rotate the valve rotor 20 to close the water passage. And a fully open state (c) that forms a water channel that makes full use of each nozzle amount. Further, the striker distance in the striker block 28 is selected.
By setting l ₁ , l ₂ , l ₃ to the nozzle pitch ± Δl,
It is possible to control the nozzle injection amount for each adjacent nozzle to a different value.

Next, a control condition calculation flow of the cooling calculation / control device 12 will be described with reference to FIG. Note that the cooling operation / control device 12 is indicated by a dashed line.

First, the material to be cooled (steel plate) given by the host computer 14
Operating conditions such as steel type, size, cooling start temperature, cooling rate, cooling completion temperature, and the representative temperature in the width direction temperature distribution on the inlet side of the cooling zone obtained from the inlet side temperature calculating device 11 (for example, Temporarily set cooling conditions (cooling water amount, water ratio, water passing speed) at the center in the width direction based on the surface temperature) (block 30). Next, after calculating the amount of cooling water and the passing speed at the center of the plate width in each cooling zone (block 31), it is determined whether or not the previously given cooling speed and cooling completion temperature match the calculation results. (Block 32), the cooling condition at the center of the plate width is determined if they match (Block 3)
Four). If they do not match, the cooling condition is changed again and the process returns to block 30. When the cooling conditions are determined, a change in temperature (temperature drop) from the start of cooling at the center of the plate width is also obtained. Note that the cooling start temperature given by the host computer 14 is a target value calculated from the finished rolling temperature, and there is a difference between the cooling start temperature and a value calculated by an input from the inlet thermometer 8 which is an actual temperature. Performs the correction operation again.

Next, the width-directional nozzle flow rate control pattern according to the measured values of the inlet side width direction temperature of the steel plate and the cooling condition of the plate width central portion,
That is, the water amount control pattern for each of the upper and lower nozzles is provisionally set (block 35), and based on this, the cooling near the plate width side end is calculated, and the upper and lower usage amounts of the nozzle flow control device and the nozzle flow control are controlled. The quantity is calculated (block 36). Here, the transition of the temperature change from the start of cooling in the vicinity of the end portion on the sheet width side is obtained.

When the nozzle flow control pattern in the vicinity of the end on the plate width side is finally determined, the following process is performed. First, for the vicinity of the outermost end of the steel sheet (approximately 30 mm from the sheet width), the temperature TN from the start of cooling of the sheet width center temperature obtained in the block 34 described above.
(I) is compared with the corresponding temperature TA (i) from the start of cooling near the outermost end, and the absolute amount of the temperature difference is equal to or less than the target value ΔT (i), ie, | TN (i) −TA (i) | ≦ ΔT
The amount of use of the nozzle flow rate control device and the number of nozzles having a nozzle flow rate of zero near the outermost end of each nozzle flow control device are obtained (block 37). If the absolute amount of the temperature difference does not become equal to or smaller than the target value ΔT (i), the nozzle flow control pattern is changed (block 38) and the cooling calculation block is performed again.
Return to 36.

Similarly, the temperatures TB (i), TC (i), TC (i), since the start of the cooling, at the temperature near the side end, that is, at the position corresponding to B, C, and D in FIG.
TD (i) and temperature TN from the start of cooling of the temperature at the center of the plate width
(I) and | TN (i) −TB (i) | ≦ ΔT
(I), | TN (i) −TC (i) | ≦ ΔT (i), | TN
(I) -TD (i) | ≦ ΔT (i) The flow rate of each nozzle is determined, and the control amount of the nozzle flow rate control device is determined (block 39). When the width direction nozzle flow rate control pattern is finally determined in this way, the flow rate of each nozzle in the cooling zone is individually controlled according to the determined width direction nozzle flow rate control pattern (block 40). Next, the outlet temperature distribution is input from the outlet temperature distribution calculating device 13 to determine whether the actual temperature distribution is equal to or less than the target value (block 41).
If it becomes the following, the cooling operation control operation ends at that point. If the target value has been exceeded, the cooling calculation is corrected again to calculate a new coefficient (block 42), and the process may be restarted from the beginning according to a normal learning control method.

In the above, i represents the elapsed time from the start of cooling. ΔT (i) is practically ΔT near the transformation point.
(I) = + 70 to + 10 ° C., ΔT (i) = + 30 when cooling is completed
The temperature may be set to ~ -10 ° C. Furthermore, TN (i) at the center of the board width
The number of temperature calculation points near the end portion on the plate width side to be compared with may be arbitrarily increased or decreased according to the actual plate width.

When obtaining the control amount of the nozzle control device from the nozzle flow rate in the vicinity of the steel sheet side end, the rotation angle of the lever 23 at which a predetermined nozzle flow rate is obtained from the flow rate characteristics of the nozzle flow control valve element 22 obtained in advance. Then, the control amounts of the position of the striker block and the distances l ₁ , l ₂ , l ₃ between the strikers are determined so that the rotation angle of each lever is the determined angle.

In order to make the temperature distribution in the plate width direction uniform at the time of completion of cooling, it is necessary to increase the discharge flow rate in steps A, B, C, and D as shown in FIG. However, practically, for example, A nozzle = 0%, B nozzle = 50
%, C nozzle = 75%, D to N nozzle = 100%, the fixed inclination amount can almost achieve the purpose. In this case, l ₁ , l ₂ , l ₃ are predetermined inclination angles. What is necessary is just to give a fixed value so that it may become the nozzle flow rate having.

Next, using the cooling device described above, 25 mm x 3,000 mm x 40,00
A method for cooling a 0 mm hot steel plate will be described.

 The cooling conditions are as follows.

Cooling start temperature; 750 ° C Cooling complete temperature; 450 ° C Cooling time; 11 seconds As shown in FIG.
And vertically between the restraining roll 3 and in the plate width direction
They were arranged at intervals of 75 mm. The amount of water injected for each nozzle is shown in Table 1 together with the conventional method. The passing speed was 60 m / min.

In order to measure the temperature of the steel sheet upon completion of cooling, the temperature in the sheet width direction at the position shown in FIG. 10 was measured. The temperature measurement results and the measured values of the steel sheet deformation are shown below Table 1 in comparison with the conventional method.

The temperature difference of the conventional method is up to 25 ° C and the deformation of the steel sheet is 8mm, whereas in this embodiment the temperature difference is up to 5 ° C and the deformation of the steel sheet is 2mm
It can be seen that it is greatly improved. As can be seen from Table 1, in this embodiment, compared to the conventional method, there is a considerable number of nozzles with a zero water injection amount, which is also energy saving.

(Effects of the Invention) As described above, the method for cooling a hot steel sheet according to the present invention is characterized in that, when forcibly cooling a hot-rolled hot steel sheet, the temperature deviation in the sheet width direction before cooling and the sheet width direction generated during cooling. By performing uniform cooling in the sheet width direction with the temperature deviation due to uneven cooling of the steel sheet corrected, it is possible to realize a cooling method for a steel sheet having a uniform temperature distribution in the sheet width direction during cooling and upon completion of cooling.
The following effects can be obtained.

(1) A steel plate having a uniform strength distribution in the plate can be obtained.

(2) A steel sheet having a good shape after cooling can be obtained.

(3) It is possible to obtain a steel sheet which has little residual stress in the sheet after cooling and has little occurrence of warpage or the like even if the steel sheet is cut into a slit shape after cooling.

(4) The flow rate of the nozzle disposed outside the plate width of the material to be cooled can be reduced to zero, and unnecessary cooling water is not flown, thereby saving energy.

[Brief description of the drawings]

FIG. 1 is a view showing the overall configuration of a cooling apparatus according to one embodiment of the present invention, FIGS. 2 and 3 are views showing a mechanism for increasing / decreasing a nozzle water injection amount, and FIG. FIG. 5 is a diagram showing the relationship between the plate width and the water width pattern in the plate width direction, FIG. 6 is a diagram showing the effect of the cooling rate and the cooling completion temperature on the supercooling of the plate side end, FIG. 7 is a diagram showing a flow of controlling a water injection amount in one embodiment of the present invention, FIG. 8 is a diagram showing a relationship between a nozzle lever angle and a nozzle injection amount, and FIG. 9 is one embodiment of a nozzle arrangement in a spray device. Figure showing an example, 10th
Fig. 11 shows the arrangement of the outlet thermometer, Fig. 11 shows the temperature of the steel sheet when cooling is completed with or without the cooling water shutoff function, and Fig. 12 shows the conventional cooling water shutoff pattern and the steel sheet when cooling is completed. It is a figure showing temperature. DESCRIPTION OF SYMBOLS 1 ... Hot steel plate, 2 ... Conveying roll, 3 ... Constraining roll, 4 ... Spray device, 5 ... Water control valve, 6 ... Water supply pipe, 7 ... Header, 8 ... Inlet temperature 9… Outgoing thermometer 10… Cooling device 11… Incoming temperature computing device 12
…… Cooling calculation and control device, 13 …… Outlet temperature calculation device, 14
… Host computer, 15… Rotation speed detector, 21… Nozzle header, 22… Valve body, 23… Lever, 24… Nozzle branch pipe, 25… Nozzle, 26… Bearing, 27… Screw axis,
28 …… Striker block, 29 …… Drive device, 29a…
... Rotation speed detector.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hidetaka Ageo 1 Nishinosu, Oita, Oita, Nippon Steel Corporation Oita Works (72) Inventor Jun Akimoto 1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu-shi, Fukuoka Prefecture -1 Inside Nippon Steel Corporation Yawata Works (56) References JP-A-59-30412 (JP, A) JP-A-48-46554 (JP, A) JP-A-58-90314 (JP, A)

Claims (1)

(57) [Claims] A hot steel sheet is passed through a plurality of cooling zones while being transported in a longitudinal direction on a hot steel sheet transport line.
A cooling method in which cooling water is sprayed on the steel sheet from a number of nozzles arranged so as to be directed to the sheet surface along the upper and lower sheet width directions and the longitudinal direction of the hot steel sheet in the cooling zone, thereby cooling the steel sheet. Based on the measured value of the representative temperature at the zone entrance side and the predetermined cooling rate and cooling completion temperature, the cooling conditions in each cooling zone for the central portion of the plate width and the temperature change from the start of cooling in the central portion of the plate width are calculated and determined. Next, the temperature change from the start of cooling in the vicinity of the end portion of the sheet width is calculated based on the measured value of the temperature in the width direction on the entry side of the steel sheet, the cooling condition in the center part of the sheet width, and the temporarily set width direction nozzle flow rate control pattern. Comparing the temperature change from the start of cooling in the center portion of the sheet width and the corresponding temperature change from the start of cooling in the vicinity of the end portion on the side of the sheet width, the absolute amount of the temperature difference is set to the target value. A method for cooling a hot steel sheet, comprising: determining a width-directional nozzle flow rate control pattern to be below, and individually controlling the flow rate of each nozzle in the cooling zone according to the determined width-directional nozzle flow rate control pattern. .