JPH08215734A - Uniformly cooling method of steel plate - Google Patents

Abstract

PURPOSE: To prevent the defective shape by adjusting the water amount from nozzles based on the calculated value of the surface temperature distribution of the lower surface of the steel plate during the rolling corrected from the surface temperature distribution of the upper surface and the temperature distribution in the width direction to unify the surface temperature of the steel plate. CONSTITUTION: The surface temperature distribution of the upper surface of the steel plate 2 is measured by surface scanning type radiation thermometers 4, 4' before or behind a finishing mill 1, while the temperature distribution in the width direction of the lower surface is measured by radiation thermometers 5, 5. The results of measurements are received by an analysis and control device 6, the range of the non- uniform temperature which is higher than the prescribed surface temperature of the steel plate 2 by the prescribed value is established, and the required amount of the cooling water is calculated taking into consideration the steel kind, the thickness, the difference between the set temperature and the measured temperature. The temperature of the steel plate 2 is unified by continuously controlling the water amount of upper surface and lower surface cooling nozzles 8, 8', and 11, 11' installed in the width direction, and the defective shape of the steel plate in an accelerated cooling equipment after the rolling is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures the temperature of the upper and lower surfaces of a steel plate during finish reverse rolling in a thick steel plate rolling line, controls the cooling of the steel plate based on the temperature measurement results, and finishes the rolling. The present invention relates to a method for cooling a steel sheet that eliminates uneven temperature distribution on the upper and lower surfaces of the steel sheet.

[0002]

2. Description of the Related Art In recent years, in a steel plate manufacturing process such as a thick steel plate, a device capable of carrying out accelerated cooling (controlled cooling) to obtain a steel plate of high strength and high toughness by quenching by quenching water-cooled steel plate by water cooling. Steel plate manufacturing equipment (accelerated cooling equipment) equipped with is operating widely.

Conventionally, in order to increase the strength and toughness of a steel sheet, it has been carried out by increasing the additive element components, but the amount of expensive additive elements can be reduced and the manufacturing cost can be greatly reduced. In addition, since it is possible to manufacture a steel sheet having excellent weldability, the application of this technology that combines controlled rolling and accelerated cooling is steadily increasing.

However, when the accelerated cooling device is used to carry out such a method, there is a problem that a defective shape of the steel sheet occurs. The causes are assumed to be as follows.

Non-uniformity of slab heating in the heating furnace before rolling occurs, temperature non-uniformity occurs during rolling of the steel sheet further upstream of the accelerated cooling device, and in the accelerated cooling device This is because the cooling from the upper and lower surfaces of the steel plate during the accelerated cooling is unbalanced.

Conventionally, various techniques have been disclosed in order to eliminate such a defective shape. The method disclosed in Japanese Examined Patent Publication No. 6-65722 measures the steel plate surface temperature on the upper surface side and the steel plate surface temperature on the lower surface side immediately before cooling, and in consideration of the temperature difference, operates in advance for each cooling zone. While maintaining the total flow rate of the upper surface side cooling water flow rate and the lower surface side cooling water flow rate set from the schedule, the cooling is performed by correcting the water amount ratio with respect to the upper and lower surface side cooling water flow rates.

Japanese Patent Laid-Open No. 60-36625 discloses a method of measuring a temperature distribution of a steel sheet immediately after hot rolling, and then partially cooling the steel sheet to eliminate the non-uniformity of the temperature in the steel sheet, and then to a specific temperature. As described above, a method of water cooling is disclosed. The method disclosed herein measures the temperature distribution on the front and back surfaces of the steel sheet using a scanning radiation thermometer while the steel sheet at 700 to 900 ° C. is being conveyed by a conveying roller immediately after hot rolling, and the measured value is The treatment is performed to cool a part of the steel sheet having a high temperature by a cooling device having a large number of cooling water nozzles to make the temperature distribution of the entire steel sheet uniform.

[0008]

However, in the method disclosed in Japanese Examined Patent Publication No. 6-65722, the unevenness of the temperature of the steel sheet during the heating furnace and rolling causes the unevenness of the upper and lower surfaces of the steel sheet even after rolling. Since the remaining non-uniformity of the temperature in the existing plate surface is carried into the accelerated cooling device, the non-uniformity of these temperatures is promoted and the defective shape is easily caused.

In the method disclosed in JP-A-60-36625, the temperature distribution of the steel sheet immediately after hot rolling is measured, and the partial cooling is carried out to eliminate the non-uniformity of the temperature in the steel sheet. However, there is a problem that the temperature non-uniformity accumulated in the steel sheet cannot be completely eliminated only by eliminating the temperature non-uniformity immediately after rolling.

Therefore, an object of the present invention is to provide a cooling method capable of completely eliminating the temperature non-uniformity accumulated in the steel sheet at the end of rolling.

[0011]

[Means for Solving the Problems]

(1) The invention of claim 1 provides a uniform cooling method for a steel sheet, which comprises the following steps. (A) During finish rolling using a finish rolling mill in which a large number of water quantity adjustable nozzles are arranged in the width direction of the steel sheet in front of and / or behind the finish rolling mill of the thick steel plate rolling mill, The lower surface obtained by measuring the upper surface temperature distribution and the lower surface widthwise temperature distribution of the steel sheet, and (b) correcting the upper surface temperature distribution and the lower surface widthwise temperature distribution of the steel sheet. According to the calculated value of the temperature distribution, the amount of water from a number of water amount adjustable nozzles installed in the width direction of the steel plate is temporally adjusted, and the surface temperatures of the upper and lower surfaces of the steel plate in the longitudinal and width directions are made uniform. To do.

(2) In the invention of claim 2, the surface temperature distribution of the upper surface of the steel sheet is measured by a surface scanning radiation thermometer, and the temperature distribution in the width direction of the lower surface of the steel sheet is measured by a radiation thermometer. 2. The measurement is performed by scanning in a direction.
A method for uniformly cooling a steel sheet according to claim 1 is provided.

[0013]

[Function] With a thermometer that can measure the surface temperature distribution of the steel sheet,
Measure the temperature distribution on the entire upper surface of the steel sheet during rolling, and at the same time measure it with a thermometer that can measure the temperature distribution in the width direction of the lower surface of the steel sheet. it can.

Therefore, during rolling, the amount of water from the nozzles provided in the rolling mill can be adjusted based on the temperature distribution on the entire upper and lower surfaces of the steel sheet, so that temperature non-uniformity does not accumulate, and therefore even at the end of rolling, The temperature can be made uniform over the entire upper and lower surfaces of the steel sheet. The temperature distribution on the entire lower surface of the steel sheet is calculated because the roll group is located on the lower surface side, and it is difficult to use a thermometer capable of measuring the surface temperature distribution.

Now, let T _U be the surface temperature distribution of the entire upper surface of the steel sheet during rolling measured by a thermometer capable of measuring the surface temperature distribution, and at the same time, the widthwise temperature of the lower surface of the steel sheet measured by a thermometer capable of measuring the line temperature distribution. Let t _D. Here, when an arbitrary point on the surface of the steel sheet is used as a reference and x _i and y _j are positions in the width direction and the longitudinal direction of the steel sheet surface respectively, T _U and t _D can be expressed as follows.

T _U = f ₁ (x _i , y _j ) t _D = f ₂ (x _i ), where y = y _j .

Since the surface temperature of the steel sheet is measured after each rolling is finished and when the rolling is once stopped, it is considered that the upper and lower surfaces of the steel sheet are reheated to have an approximate temperature distribution. Therefore,
The surface temperature distributions of the lower surface of the steel plate and the upper surface of the steel plate are considered to be exactly the same although there is a constant temperature difference.

Therefore, the average value of the temperature distribution in the width direction of the lower surface of the steel sheet (∫t _D dx / x) and the average value of the temperature distribution in the width direction immediately above the measurement point of the lower surface of the surface temperature distribution of the upper surface of the steel sheet (∫T
The surface temperature distribution T _D of the lower surface of the steel plate can be obtained by obtaining the ratio α with _U dx / x). That is,

Α∫T _U dx / x = ∫t _D dx / x, where y = y _j for both. T _D = αT _U = αf ₁ (x _i , y _j )

In order to improve productivity and obtain high flatness, it is desirable to use a surface scanning type radiation thermometer capable of quick and highly accurate measurement. For example, a VS2000 series radiation thermometer manufactured by Nippon Avionics can be used.
Also, as a thermometer that can measure the temperature distribution in the width direction of the steel sheet, an ordinary radiation thermometer is used, the detection end of the optical fiber is connected to this, and the detection end of this optical fiber is mechanically moved in the width direction of the steel sheet. The temperature distribution on the back surface side of the steel sheet can be measured.

[0021]

FIG. 1 shows an embodiment of a thick steel plate finishing rolling line for carrying out the method of the present invention. In the figure, 1 is a finish rolling mill, 2 is a steel plate, 3 is an accelerated cooling device, 4 and 4'are surface scanning type radiation thermometers, 5 and 5'are normal radiation thermometers, and 6 are analysis and
Control device, 7, 7'is a top surface cooling nozzle header, 8,
8'is an upper surface cooling nozzle, 9 and 9'is an upper surface cooling flow control valve, 10 and 10 'is a lower surface cooling nozzle header, 1
Reference numerals 1 and 11 ′ are lower surface cooling nozzles, and 12 and 12 ′ are lower surface cooling flow control valves.

During the rolling, the surface temperature distribution of the upper surface of the steel sheet 2 exiting the finishing rolling mill 1 is measured by the surface scanning type radiation thermometers 4 and 4 ′ provided above the finishing rolling mill 1. At the same time, the temperature distribution in the width direction of the lower surface of the steel sheet 2 is measured by the radiation thermometers 5 and 5'from the lower surface of the rolling line. These temperature measurement results are sent to the analysis / control device 6.

This apparatus obtains the surface temperature distribution of the lower surface of the steel sheet 2 by the calculation method already described, and based on the temperature distribution of the upper and lower surfaces of the steel sheet 2 actually measured or calculated in this way, the front of the finish rolling mill 1 and It has a function of adjusting and controlling the amount of water from the upper and lower cooling nozzles 8, 8'and 11, 11 'provided at the rear side separately.

Here, the adjustment control of the water amount is performed as follows. First, with respect to the set temperature of the surface of the steel sheet 2 at the time of rolling, the range of temperature nonuniformity that is higher by at least 20 ° C. or more than that is determined. Next, with respect to the determined non-uniform range of the high temperature, the steel type of the steel plate 2, the plate thickness during rolling, the speed of the steel plate 2 passing through the cooling device, and the set temperature during rolling and the measured temperature Calculate the required amount of cooling water in consideration of the differences.

Based on the result of this calculation, the water amounts of the upper and lower surface cooling nozzles 8, 8'and 11, 11 'whose water amounts can be controlled independently in the width direction are continuously measured as the steel plate 2 passes. By changing the temperature, the temperature can be made uniform. The water volume control of the nozzles 8, 8'and 11, 11 'is performed by the respective flow rate control valves 9, 9'and 12,
12 '.

As described above, since the steel sheet 2 is always subjected to the cooling control based on the temperature distribution of the entire upper and lower surfaces of the steel sheet 2 during rolling, the temperature of the steel sheet 2 becomes nonuniform even at the end of rolling. There is no such thing.

In the thick steel plate finishing rolling line shown in FIG. 1 provided with the cooling nozzle shown in Table 1, the steel material shown in Table 1 is actually rolled according to the method of the present invention, and the temperature with respect to the target cooling stop temperature after accelerated cooling. The deviation was investigated. Table 2 shows the results. In addition, Table 2 also shows the results of Comparative Examples performed without using the cooling method of the present invention.

As is apparent from Table 2, when rolling is performed using the cooling method of the present invention and then accelerated cooling is performed, the non-uniformity of temperature generated during heating and the non-uniformity of temperature generated during rolling are eliminated. Therefore, the temperature deviation with respect to the target cooling stop temperature at the time of accelerated cooling was −17 ° C. to + 20 ° C., which was significantly improved as compared with −40 ° C. to + 43 ° C. of the comparative example, and no defective shape occurred.

Although a flat spray nozzle is used as the cooling nozzle in this embodiment, a pipe laminar nozzle may be used. Further, the cooling device may be installed near the rolling mill as in this embodiment, or a descaling nozzle attached to the rolling mill may be used.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

As is clear from the above description, the cooling method of the present invention prevents the temperature non-uniformity from accumulating during rolling. A wide temperature distribution can be obtained. As a result, it is possible to completely prevent the occurrence of a defective shape of the steel sheet during accelerated cooling after rolling.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a finish rolling line for thick steel plates for carrying out the method of the present invention.

[Explanation of symbols]

 1 Finishing Roller 2 Steel Plate 3 Acceleration Cooling Device 4 Surface Scanning Radiation Thermometer 4'Surface Scanning Radiation Thermometer 5 Radiation Thermometer 5'Radiation Thermometer 6 Analysis / Control Device 7 Top Cooling Nozzle Header 7'Top Cooling Nozzle Header 8 Top Cooling Nozzle 8'Top Cooling Nozzle 9 Top Cooling Flow Control Valve 9'Top Cooling Flow Control Valve 10 Bottom Cooling Nozzle Header 10 'Bottom Cooling Nozzle Header 11 Bottom Cooling Nozzle 11' Bottom Cooling Nozzle 12 Flow control valve for lower surface cooling 12 'Flow control valve for lower surface cooling

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Munehiro Ishioka 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (2)

[Claims] 1. A uniform cooling method for a steel sheet, comprising the following steps. (A) During finish rolling using a finish rolling mill in which a large number of water quantity adjustable nozzles are arranged in the width direction of the steel sheet in front of and / or behind the finish rolling mill of the thick steel plate rolling mill, The surface temperature distribution of the upper surface and the temperature distribution of the lower surface of the steel plate in the width direction are measured, and (b) the surface temperature distribution of the lower surface obtained by correcting the surface temperature distribution of the upper surface and the temperature distribution of the lower surface of the steel plate in the width direction. According to the calculated value of the temperature distribution, the amount of water from a large number of water amount adjustable nozzles installed in the width direction of the steel plate is temporally adjusted, and the surface temperatures of the upper and lower surfaces of the steel plate in the longitudinal direction and the width direction are made uniform. . 2. A surface temperature distribution on the upper surface of the steel sheet is measured by a surface scanning radiation thermometer, and a temperature distribution in the width direction of the lower surface of the steel sheet is measured by scanning the steel plate in the width direction with a radiation thermometer. The uniform cooling method of the steel sheet according to claim 1.