JP2001300627A - Method for cooling thick steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling method of a thick steel plate for improving the flatness in the shape of the steel plate and uniformalizing material qualty by a simple method. SOLUTION: This method is a method for performing the controlled cooling 22 of the thick steel plate 1 after finish rolling in a thick steel plate manufacturing process, the distribution of scale thickness is measured 14 and, after reducing variation in the scale thickness to <=10 μm by descaling 16 or applying a surface film based on the measured result, the controlled cooling 22 is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cooling a steel plate in manufacturing a steel plate.

[0002]

2. Description of the Related Art Recently, in the production of thick steel plates, strength and weldability have been improved by controlled cooling after finish rolling. In controlled cooling, it is necessary to perform cooling so that the temperature distribution in the plate width direction becomes uniform in order to obtain uniform material properties and flatness. For this purpose, many cooling methods have been proposed. For example, JP-A-6-328118, JP-A-6-328118
A cooling method according to JP-A-330155 or JP-A-7-256331 is known.

[0003] The cooling method disclosed in Japanese Patent Application Laid-Open No. 6-328118 discloses a method of rolling high-strength steel by rolling a thick steel plate by a controlled cooling device and then cooling the steel plate during or before rolling.
Utilizing a descaling device or other device to control the scale removal range in the width direction of the steel sheet and further control the residual thickness of the scale to change the heat transfer coefficient in the width direction of the steel sheet surface, Uniform steel plate shape and material.

[0004] In the cooling method disclosed in Japanese Patent Application Laid-Open No. 6-330155, in the controlled cooling of a thin thick steel sheet, the thickness of the scale on the steel sheet is adjusted by adjusting the pressure of high-pressure water of a scale removing device attached to a rolling mill. By controlling the heat transfer coefficient on the surface of the steel sheet, the mechanical properties in the longitudinal direction of the steel sheet are made uniform.

Further, a cooling method disclosed in Japanese Patent Application Laid-Open No. Hei 7-256331 is a controlled cooling method for a thick steel plate which obtains a uniform material in the width direction and a good flatness of the steel plate. Disclosed is a method of measuring the scale thickness distribution on the surface, cooling the water after controlling the water injection position and the amount of injected water of the scale removing device so that the measured value matches the target value of the scale thickness distribution on the steel plate surface. Have been.

JP-A-6-328118, JP-A-6-328118
In any of the cooling methods disclosed in JP-A-330155 or JP-A-7-256331, the cooling is controlled by controlling the surface properties of the steel material to be cooled, particularly the scale thickness. In this control, in order to control the surface texture on the steel sheet side, changes in the amount of scale that grows from rolling to cooling are ignored, and contact with the table roller on the steel sheet surface during transport during this time is ignored. It is not possible to control the scale thickness as intended before controlled cooling, such as the occurrence of peeling of the scale grown after the rolling mill. Also,
When control cooling is performed after straightening after rolling, scale peeling occurs in the straightening machine, and the scale thickness distribution tends to vary, so that uniform cooling control is difficult.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for cooling a thick steel plate capable of improving the flatness of the shape of the steel plate and making the material uniform.

[0008]

According to a first aspect of the present invention, there is provided a method for cooling a thick steel plate in a method for controlling and cooling a thick steel plate after finish rolling in a thick steel plate manufacturing process. After controlling the dispersion of the scale thickness to 10 μm or less based on the descaling or the surface film coating based on the above, the controlled cooling is performed.

By setting the variation of the scale thickness to 10 μm or less, the cooling rate becomes uniform and the steel sheet is cooled uniformly. As a result, thermal distortion due to non-uniform surface temperature of the steel sheet is reduced, and a good steel sheet shape is obtained.

A method of cooling a thick steel sheet according to a second invention is a method of controlling and cooling a thick steel sheet after finish rolling in a steel sheet manufacturing process, wherein the scale thickness distribution is measured, and the scale thickness is scaled by descaling based on the measurement result of the scale thickness distribution. After the thickness is reduced to 10 μm or less, controlled cooling is performed.

By setting the scale thickness itself to 10 μm or less, the cooling rate becomes uniform, uniform cooling can be performed, and the plate shape becomes uniform.

[0012]

FIG. 1 shows an example of equipment for carrying out a method for cooling a steel plate according to the present invention. As shown in FIG. 1, a hot straightening device (roller leveler) 12, a scale thickness measuring device 14, and a descaling device 16 are arranged on the exit side of the finishing mill 10. As the scale thickness measuring device 14, for example, a laser distance meter is used, and the steel plate surface is scanned to measure the scale thickness. The descaling device 16 is of the high pressure water spray type. The scale thickness distribution measuring device 14 is connected to a descaling device 16 via a descaling control device 18. The descaling control device 18 outputs a control signal to the descaling device 16 based on the measurement result of the scale thickness. A steel plate surface temperature measuring device 20 is arranged between the descaling device 16 and the control cooling device 22. The steel plate surface temperature measuring device 20 uses a radiation thermometer, and measures the steel plate surface temperature. The control cooling device 22 adjusts the cooling speed and the cooling stop temperature of the steel sheet 1 based on the measurement result of the steel sheet surface temperature. In addition, a heating furnace, a rough rolling mill, and the like as main devices on the upstream side of the finishing mill 10 (all are not shown).
Is arranged.

[0013] The hot straightening device 12 is a steel plate 1 after finish rolling.
In addition to correcting the shape defect of the steel sheet to flatten the steel sheet, a part of the scale is peeled off, or the scale peeling in the descaling 16 is assisted. FIG. 2 shows a state in which a part of the scale 5 is peeled off by the hot straightening and the steel sheet surface 2 is exposed. For example, the thickness of the peeled scale is 10 to 40.
μm, width 50-300 mm, length 100-100,000
It is about 0 mm.

The descaling control unit 18 determines the scale thickness to be removed based on the scale thickness signal from the scale thickness measuring unit 14, and
6 to output a descaling control signal. The descaling device 16 adjusts the variation of the scale thickness with the injection position and the injection water pressure based on the descaling control signal. In the present invention, as described above, the controlled cooling is performed after the variation in the scale thickness is 10 μm or less, or the scale thickness on the surface of the thick steel plate is 10 μm or less. Variation in scale thickness is represented by the difference between the maximum scale thickness and the minimum scale thickness. When the steel plate surface is exposed, the maximum scale thickness becomes a variation in the scale thickness. Note that the approximate scale thickness of the scale peeled portion can be estimated by various rolling conditions. For example, when the temperature of the steel sheet before cooling is 780 ° C., the scale thickness of the part that has not been separated is 2
0 to 40 μm, and the scale thickness of the peeled portion is 5
１５15 μm.

By reducing the variation in scale thickness, the cooling rate is made uniform and the steel sheet is cooled uniformly.
Therefore, thermal distortion due to non-uniform surface temperature of the steel sheet is reduced, and a good steel sheet shape is obtained. Since the cooling rate is high when there is a scale, it is more efficient for uniform cooling to reduce the variation in scale thickness. If the variation in the scale thickness is 10 μm or less, the temperature difference due to the variation in the scale thickness is 20 ° C. or less, as shown in FIG. When the temperature difference is 20 ° C. or less, a steel sheet having a good flatness can be obtained.

FIG. 4 shows a facility in which the variation in scale thickness is substantially reduced to 10 μm or less by coating a surface film. 4 is obtained by replacing the descaling device 16 of FIG. 1 with a surface film coating device 24 and replacing the descaling control device 18 with a surface film coating control device 26.

The scale thickness distribution is measured in advance by a scale thickness measuring device. When the measurement position of the scale thickness moves to the position of the surface film coating device 24,
A powdery surface film material is sprayed from the surface film coating device 24 based on the measurement result, and a surface film is formed on a portion where the scale thickness is small. As a surface film material, a material having a similarity of scale roughness and surface thermophysical properties, for example, silicon-based, alumina-based,
Oxide ceramic heat resistance such as zirconia and magnesia, ceramic heat resistance paint such as boron nitride and silicon nitride, glass heat resistance paint, and the like are used. The thickness of the applied surface film is such that the variation in the scale thickness is 10 μm or less. FIG. 5 shows that the surface film 7
Shows a state in which is formed. By forming a surface film on a peeled portion or a thin portion of the scale, roughness and thermal inertia can be made uniform and uniform cooling can be performed. Thereby, the flatness of the shape can be improved.

The equipment when the scale thickness itself is 10 μm or less is the same as the equipment shown in FIG. Figure 3 above
As is clear from the above, when the thickness of the scale itself is 10 μm or less, the temperature difference at the time of water cooling stop is 20 ° C. or less. As a result, the cooling rate becomes uniform, uniform cooling can be performed, and the plate shape becomes uniform. When it is necessary to suppress the variation in the surface temperature of the steel sheet within 10 ° C., the variation in the scale thickness may be set to 5 μm or less.

As described above, there are a method of peeling the scale and a method of applying a surface film to adjust the thickness of the scale. However, the former method has a higher cooling rate and the latter method has a lower rate.

[0020]

EXAMPLE A thick steel plate having a thickness of 30 mm and a width of 3000 mm was rolled by a finishing mill, passed through a hot straightening machine, and the surface temperature of the steel sheet was measured with a radiation thermometer.
Cooled to ° C. Immediately before controlled cooling, the steel sheet was descaled. The descaling conditions in this case were: nozzle water pressure: 10 MPa, water amount per nozzle: 170 l / min., Number of nozzles: distance between steel plate and nozzle: 250 mm, injection angle: 15 degrees. As a result, the scale thickness becomes 1
It was possible to reduce it to 0 μm or less. Thereafter, controlled cooling was performed by a controlled cooling device. As a result, the temperature distribution became uniform as shown in FIG. In FIG. 6, (a) shows the steel sheet surface temperature distribution when the scale thickness is not adjusted, and (b)
Shows the steel sheet surface temperature distribution when the scale thickness is adjusted by descaling to reduce the variation. FIG. 7 shows the flatness of the steel sheet after controlled cooling.
The present invention is compared with a comparative example. The variation of the scale thickness in the case of the present invention is 10 μm, and that of the comparative example is 20 μm. When the method of the present invention is used, the flatness is improved as compared with the conventional method, and the rejection rate due to the shape defect is 15%.
% To 5%.

[0021]

As described above, by adopting the method for cooling a thick steel plate according to the present invention, the temperature of the steel plate can be made uniform by a simple method, thereby improving the flatness of the steel plate shape. The material can be made uniform.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of equipment for implementing the present invention.

FIG. 2 is a longitudinal sectional view schematically showing a scale peeling portion.

FIG. 3 is a graph showing the relationship between scale thickness and stop temperature.

FIG. 4 is a schematic configuration diagram of another facility for implementing the present invention.

FIG. 5 is a longitudinal sectional view schematically showing a state where a surface film material is applied to a scale peeling portion.

6 (a) is a graph showing the steel sheet surface temperature distribution when the scale thickness adjustment is not performed, and FIG. 6 (b) is a graph showing the steel sheet surface temperature distribution when the scale thickness adjustment is performed.

FIG. 7 is a diagram showing a decrease in rejection rate due to a reduction in scale thickness variation.

[Description of Signs] 1 Thick steel plate 2 Steel plate surface 5 Scale 10 Finishing mill 12 Hot straightening device 14 Scale thickness distribution measuring device 16 Descaling device 18 Descaling control device 20 Steel plate surface temperature measuring device 22 Control cooling device 24 Surface film Coating device 26 Surface film coating control device

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // C21D 1/00 123 C21D 1/00 123A (72) Inventor Nobuhiko Madama 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Inside the Kimitsu Works (72) Inventor Osamu Akutsu 1 Kimitsu, Kimitsu City, Chiba Prefecture Inside Nippon Steel Works Ltd. F-term (reference) in Oita Works 4K034 BA05 CA01 DA06 DA08 DB03 FA05 FB03 4K044 AA02 AB02 BA11 BA13 BA14 BA18 BB01 BC12 CA21

Claims (2)

[Claims] In a method of controlling and cooling a thick steel plate after finish rolling in a thick steel plate manufacturing process, a scale thickness distribution is measured, and the scale thickness variation is reduced by descaling or surface film coating based on the measurement result of the scale thickness distribution. A method for cooling a thick steel plate, wherein the thickness is controlled to 10 μm or less, followed by controlled cooling. 2. A method for controlling and cooling a thick steel plate after finish rolling in a thick steel plate manufacturing process, wherein the scale thickness distribution is measured, and the scale thickness is reduced to 10 μm or less by descaling based on the measurement result of the scale thickness distribution. A method for cooling a thick steel plate, comprising performing controlled cooling.