JPH06184623A - Method for cooling thick steel plate - Google Patents

Abstract

PURPOSE:To uniformize the temp. in the width direction by shielding both edge parts of a thick steel plate from water flow at the time of diagonally jetting the high-pressure water flow onto the thick steel plate from slit jet nozzles provided at the inlet side in a control cooling device. CONSTITUTION:By supplying the slit-shaped water flow onto the surface of the steel plate 6 from the upper slit jet nozzle 7 and the lower slit jet nozzle 8 of a forced cooling device, the steel plate 6 is rapidly cooled. A steel plate width edge part over-cooling preventing device (edge mask) 9 shields the opening parts of the slit jet nozzles 7, 8 by the prescribed widths corresponding to the steel plate width. At the time of starting the cooling, since the temp. of the plate width edge part is lower than the temp. of the width center part, the over-cooling preventing device 9 is used to reduce the cooling rate at the width edge parts and to keep the temp. in the width direction uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a desired material so as not to cause a defective shape of the hot rolled steel sheet when cooling the hot rolled steel sheet by blowing cooling water from both upper and lower surfaces. As described above, the present invention relates to a method for cooling a hot-rolled steel sheet that optimally controls the amount of cooling water injected from both sides.

[0002]

2. Description of the Related Art In recent years, high-temperature thick steel plates immediately after hot rolling are rapidly cooled (accelerated cooling) by water cooling to obtain a quenching effect and impart high strength properties to the steel plates. A steel plate manufacturing apparatus equipped with a process called controlled cooling is in operation. With this steel plate manufacturing apparatus, it becomes possible to manufacture a steel plate having excellent use performance by performing controlled cooling immediately after rolling.

However, in such a conventional steel plate manufacturing apparatus, due to an imbalance of cooling from the upper and lower surfaces of the steel plate during accelerated cooling, a shape defect due to a warp in the width direction of the plate is caused as compared with the conventional air cooling. There is a drawback that is likely to occur. The occurrence of this shape defect is due to the difference in cooling rate due to the difference in behavior of the cooling water sprayed from the upper surface and the lower surface of the steel sheet. When each part of the steel plate is cooled at different cooling rates in this way, asymmetric internal stress is generated in the plate thickness direction, which deteriorates the shape of the product.

Further, in a remarkable case, in addition to a defective shape, there is a problem that mechanical properties are different between the upper and lower surfaces. In order to prevent the occurrence of such shape defects, conventionally, the temperature of the steel plate upper and lower surfaces during water cooling is measured, the deformation amount is predicted from the temperature difference, and the water injection amount on the steel plate upper and lower surfaces is suppressed so that the deformation is suppressed. There is a technology to control. However, no method for controlling the amount of water injection is presented, and no consideration is given to the influence on the cooling end temperature when the amount of water injection to the upper and lower surfaces is changed.

The present invention has been made in view of the above-mentioned problems of the prior art, and in view of the material, a predetermined cooling end temperature is secured, and the warp amount of the hot steel sheet during water cooling is a specified value. An object of the present invention is to provide a method for cooling a hot-rolled steel sheet having a function of controlling the amount of cooling water sprayed from the upper and lower surfaces so as to be contained inside.

[0006]

The present invention for achieving the above-mentioned object advantageously solves the problems of the prior art, and in the production of thick steel plate, a predetermined rolling mill and a finish rolling mill are used. For a thick steel plate that is rolled into a size and straightened by a straightening machine and then cooled by a controlled cooling device, a high-pressure water stream is supplied from a slit jet nozzle with high cooling capacity installed on the inlet side of the controlled cooling device. The method for cooling a thick steel plate is characterized in that the water flow to both ends of the width of the thick steel plate is shielded by injecting the liquid at an angle.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the present invention. The equipment layout of the rolling line is shown. 1 is a rough rolling mill, 2 is a finish rolling mill, 3
Is a hot straightener, and 4 is a forced cooling device. Thick steel plate
It is rolled to a predetermined size by both rough and finish rolling mills, the rolling wave is straightened by a straightening mill, and then cooled by a forced cooling device. Further, the forced cooling device is divided into 6 zones, 1 zone is equipped with a slit jet nozzle cooling zone, and 2 to 6 zones are equipped with spray nozzle cooling zones. Reference numeral 5 represents a slab, and 6 represents a rolled steel plate.

FIG. 2 is a diagram of one zone of the forced cooling device according to the present invention. 7 is the upper slit jet nozzle, 8
Is a lower slit jet nozzle, which is a device that supplies a slit-like water flow to the front and back surfaces of the steel sheet to rapidly cool the steel sheet surface layer. Reference numeral 9 denotes a steel plate width end supercooling prevention device (edge mask) newly installed according to the present invention, which has a structure in which the slit jet nozzle opening is closed with a width of 400 mm to stop the water flow. Further, the structure is such that it can move in the width direction according to the width of the steel plate so that the water flow at the width end of the steel plate to be cooled can be stopped. Reference numeral 11 denotes a control system, which performs control to move the edge mask 9 in accordance with the steel plate width. The edge masks 9 are installed at a total of four places on the left and right of the upper and lower slit jets, and further, a control system is constructed so that movement in the width direction can be performed independently in the vertical direction. Further, 10 is a flow control valve, which adjusts the amount of cooling water of the steel plate according to the value instructed by the control system of 11.

FIG. 3 is a diagram showing the principle of the present invention, and is a schematic view of the temperature history during cooling of the width center part and the width end part of the steel sheet. Film boiling is dominant for a while after the start of cooling, and then it shifts to nucleate boiling and the cooling rate increases.
The broken line shows the cooling temperature history when the supercooling prevention device is not used, and the solid line shows the cooling temperature history when the supercooling prevention device is used. Further, the alternate long and short dash line is the cooling temperature history of the width center portion. At the start of cooling, the temperature at the width end of the plate is lower than that at the center of the width. This is because the width end is supercooled by air cooling that occurs from rolling to straightening. When the supercooling preventive device is not used, the slit jet in one zone is rapidly cooled in the initial stage of cooling, and the transition to nucleate boiling occurs earlier than in the central portion of the width. Therefore, the temperature difference from the center of the width is further expanded,
Even if the water flow to the width end is prevented in the subsequent zones (2nd zone and thereafter), that is, even if supercooling is prevented by some method, it is difficult to significantly reduce the temperature difference from the width center. . On the other hand, when the supercooling preventive device in one zone of the present invention is used, the cooling rate at the width end portion in the initial stage of cooling can be reduced and the transition to nucleate boiling can be delayed, so that the temperature difference from the width center portion can be reduced. It is possible to reduce the size.

FIG. 4 is a diagram showing an embodiment of the present invention, in which the vertical axis represents the steel plate temperature and the horizontal axis represents the time from the start of cooling.
As for the cooling temperature history of the steel plate width center part and the width end part, the temperature of the steel plate width end part becomes the temperature of the width center part by using the supercooling prevention device (edge mask) of the present invention as shown in FIG. We were able to improve it until it almost agreed.

[0011]

As described above, according to the cooling method of the present invention, the amount of cooling water from the upper and lower surfaces of the thick steel plate can be controlled within a suitable range at all times, and the temperature in the width direction of the thick steel plate is maintained uniform. It is possible to obtain a steel sheet of good quality.

[Brief description of drawings]

FIG. 1 is an equipment layout diagram showing an embodiment of the present invention.

FIG. 2 is a perspective view of one zone of the forced cooling device in FIG.

FIG. 3 is a diagram showing the principle of the method of the present invention.

FIG. 4 is a graph showing an implementation result of the present invention.

[Explanation of symbols]

 1 Rough rolling mill 2 Finishing rolling mill 3 Hot straightening machine 4 Forced cooling device 5 Slab 6 Steel plate 7 Upper slit jet 8 Lower slit jet 9 Edge mask 10 Flow control valve 11 Control system

Claims (1)

[Claims] 1. In the production of a thick steel plate, a controlled cooling is applied to a thick steel plate which is rolled to a predetermined size by a rough rolling mill and a finish rolling mill, a straightening machine corrects a rolling wave, and then cooled by a controlled cooling device. Cooling a thick steel plate characterized by spraying a high-pressure water stream obliquely to the thick steel plate from a slit jet nozzle having a high cooling capacity provided on the inlet side of the device to block the water flow to both widthwise ends of the thick steel plate. Method.