JPH10300301A - Method for controlling and cooling steel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a temperature deviation at the time of cooling a control cooling steel sheet by cooling the hot rolled sheet via a steel piece heating furnace with cooling water injected by steam. SOLUTION: Scale generated on the surface of a slab 4 heated by a heating furnace 1 is removed by a scale breaker 2 in a heating step, then hot roughly rolled by a roughing-down mill 3, and a thin steel sheet is obtained from a hot finish rolled steel sheet 6 by a hot finishing mill 5 by a cold mill group 8 via a hot leveler 7. In a hot rolling step in such a manufacturing process, steam of 5 kg/cm<2> is injected to the spray cooler of pressure of 8 kg/cm<2> of the control cooler of a control cooling steel material, and control cooling is executed. Thus, a temperature deviation of the steel sheet at the time of cooling can be reduced.

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 controlled cooling steel material in hot rolling, which improves the cooling speed of a steel material to be cooled, reduces the temperature deviation in the steel material during cooling, and makes the shape and the material of the steel material uniform. It is intended to aim at.

[0002]

2. Description of the Related Art Conventionally, the cooling of a controlled cooling steel material in hot rolling is very difficult because the cooling mode changes from a film boiling region to a nucleate boiling region, resulting in a large change in cooling characteristics. Met. Specifically, 600
In a high temperature range of not less than ° C., the film is cooled in a film boiling region, and a vapor film is generated between the cooling water and the steel material. In addition, when the temperature falls below the film boiling range,
It passed through an unstable transition region where film boiling and nucleate boiling coexist, and suddenly changed to a nucleate boiling region with high cooling ability. Therefore, it was very difficult to uniformly cool steel.

[0003] Therefore, in order to promote the cooling in the film boiling region, it is necessary to increase the blowing pressure of the cooling water or to increase the pressure of the cooling water.
As disclosed in Japanese Patent No. 4378, efforts have been made to spray a fluid composed of dry ice, ice, and water to break a vapor film and improve cooling capacity. For cooling in an unstable transition region where film boiling and nucleate boiling coexist, see Japanese Unexamined Patent Publication No.
As shown in Japanese Patent Application Laid-Open No. 8-71339, by controlling the temperature of the cooling water at a high temperature, a film boiling region is formed stably to a low temperature side. Efforts are being made to convert it to

[0004]

As for the promotion of cooling in the film boiling region, high pressure hydration and addition of solids to the water stream have been performed, but all of them have a problem that equipment cost and running cost increase. is there. Further, regarding stable generation up to the low temperature side of the film boiling region due to an increase in water temperature, there is a problem that the overall cooling capacity is reduced, and the conventional measures cannot be said to be the most effective.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and a method of controlling and cooling the structure of a steel material by cooling a steel material heated and rolled in a billet heating furnace, comprising the steps of: A controlled cooling method for a steel material, characterized by cooling with cooling water injected with steam. And, the temperature of the cooling water injected with steam is 70-100 °
C, which is a controlled cooling method.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 compares the temperature transition of the steel material during cooling between the conventional cooling and the cooling method according to the present invention. According to the method of the present invention, by injecting cooling water obtained by injecting steam into water onto a steel material surface and cooling the steel material, in a film boiling region, a steam film generated between the steel material and the cooling water is formed into the injected water. The so-called cavitation effect, which is generated when the generated air bubbles come into contact with the steel material, breaks the vapor film and improves the cooling capacity.
Therefore, in the film boiling region, a decrease in the heat transfer coefficient due to the vapor film, which has been a problem in the conventional water spray cooling, is eliminated, and a cooling rate higher than the conventional cooling can be obtained.

[0007] In the transition boiling region from the lower boiling region to the nucleate boiling region, steam is injected into the water, so that the temperature of the cooling water rises to about 100 ° C. It can be shifted to the low temperature side. Further, regarding cooling in the nucleate boiling region, as the water temperature increases, the cooling capacity decreases, and the cooling rate becomes slow. As a result, a rapid change in the cooling rate from the film boiling range to the nucleate boiling range is suppressed, and cooling can be performed stably from the high temperature range to the low temperature range while maintaining the entire cooling capacity.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the present technology is applied to a plate mill will be described below. FIG. 2 is an overall schematic diagram of equipment to which the present invention is applied. As shown in FIG. 2, after the slab 4 heated in the heating furnace 1 is removed by the scale breaker 2 on the slab surface during the heating process by the scale breaker 2, the rough rolling is performed by the hot rough rolling mill 3. Then, the steel plate 6 which has been hot-finished and rolled by the hot-finishing mill 5 is hot-leveler 7
After that, a thin steel plate is obtained by the cold rolling mill group 8.

In the hot rolling process in such a manufacturing process, the pressure of the control cooling device for the control cooling steel material is 8 kg / cm.
² of the spray cooling system performs steam injection 5 kg / cm ^2, was carried out controlled cooling. As the cooling conditions, controlled cooling was started at 780 to 830 ° C. and 400 to 50
Stop at 0 ° C., rolled size, 60 × 2255 × 140
The effect was evaluated for the material No. 00. As a result, the temperature deviation at the time of cooling the controlled cooling steel sheet was reduced, and the shape defect due to the temperature deviation was improved. FIG. 3 shows a comparison between the conventional method and the method of the present invention based on an index of the number of steel sheets obtained by re-correcting a steel sheet having a poor shape off-line (re-correction index). This figure also shows that the effect of the method of the present invention is remarkable.

[0010]

As described above, an important aspect of the method for cooling a controlled cooling steel material according to the present invention is that uniform cooling is performed while the cooling characteristics change greatly from film boiling to nucleate boiling. is there. For this purpose, it is possible to change the cooling in the film boiling region and the cooling in the transition region to the nucleate boiling region by cooling means, but the temperature at which the film boiling region changes to the transition boiling region depends on the surface properties of the steel. (Roughness, scale, etc.), it was difficult to control. In the present invention, the same cooling means makes it possible to smoothly change the cooling characteristic from a high temperature range to a low temperature range, and stabilizes cooling,
This is an extremely excellent effect of improving the material ratio by reducing the shape problem and the material variation caused by the cooling variation.

[Brief description of the drawings]

FIG. 1 is a diagram comparing a conventional method and a method of the present invention with respect to a temperature transition of a steel material;

FIG. 2 is an overall schematic diagram of equipment to which the present invention is applied,

FIG. 3 is a diagram comparing the conventional method and the method of the present invention with respect to the recorrection index.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Scale breaker 3 Rough rolling mill 4 Slab 5 Hot finishing rolling mill 6 Steel plate 7 Hot leveler 8 Cold rolling mill group

Claims (2)

[Claims] 1. A method for controlling and cooling a steel material which is heated and rolled in a slab heating furnace and controlled by microstructure, wherein the steel material is cooled by cooling water injected with steam. 2. The method according to claim 1, wherein the temperature of the cooling water injected with the steam is 70 to 100 ° C.
A controlled cooling method for a steel material as described above.