JPH06142750A - Method for cooling thick steel plate - Google Patents

Abstract

PURPOSE:To prevent warping upward in the finish-rolling by remarkably changing cooling water ratio at the upper and lower surfaces according to a plate thickness in the case of cooling the thick steel plate before finish-rolling. CONSTITUTION:At the time of cooling the upper surface of a thick steel plate having >=40mm thickness before the finish-rolling, by a laminar flow and the lower surface thereof by spraying, the cooling water ratio (upper/lower) on the upper and the lower surfaces is made in the range of (plate thickness (mm)/30)+ or -1.0 according to the plate thickness. In the case of cooling the thick steel plate before the finish-rolling, the thicker the plate thickness is, the larger the temp. gradient in the plate thickness direction during cooling is, and the surface temp. of the thick steel plate becomes the low temp. range having the transition boiling zone or less. According to this reason, cooling capacity of the water on the plate becomes large, and in order to compensate this difference, the cooling water ratio on the lower and upper surfaces is made to be high. The thicker the plate thickness at the time of cooling is, the larger this inclination is. By changing the cooling water ratio on the upper and the lower surfaces in this range according to the plate thickness, the rolling pass just after this cooling, can be executed and also, the warp upward can surely be prevented.

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 thick steel plate before finish rolling.

[0002]

2. Description of the Related Art Controlled rolling (hereinafter referred to as CR) is used as a method for producing a steel sheet having excellent strength and toughness.
The rolling method has been widely used. This C
The R-rolling is characterized in that the rolling temperature during rolling can be controlled accurately and the final rolling finish temperature can be set directly above the Ar ₃ temperature to refine the structure and improve the strength and toughness.

Conventionally, this CR rolling method, as shown in FIG. 2, temporarily stops rolling at a transfer thickness of a certain thickness with respect to the product sheet thickness t, and then cools by air cooling from the temperature T ₁ at that time to a predetermined temperature T _2. After that, rolling is performed again so that the final finishing temperature at the time of final rolling to obtain the predetermined plate thickness t is just above the Ar ₃ temperature.

[0004]

In the CR rolling, unlike the ordinary rolling, the rolling work is temporarily stopped during the rolling and the rolling work is cooled until the temperature of the rolled material changes from T ₁ to T _2. However, there is a problem in that the rolling efficiency is reduced.

The reduction in rolling efficiency in this CR rolling method can be prevented by intensively water-cooling a thick steel plate in a specific pass during rolling. However, when water cooling the thick steel plate before finish rolling with a specific thickness, the plate thickness during cooling is also extremely thick, and there is a problem of warpage due to the temperature decrease of the upper surface of the thick steel plate in rolling in the finish rolling thereafter, It is necessary to optimize the cooling conditions for the upper and lower surfaces of thick steel plates, that is, the ratio of upper and lower water amounts.

[0006]

The gist of the present invention is that when cooling the upper surface of a thick steel plate having a thickness of 40 mm or more before finish rolling by laminar flow and the lower surface by spraying, the water content ratio of the upper and lower surfaces ( (Bottom / Top) according to the plate thickness (plate thickness (mm) /
30) A method for cooling thick steel plates, characterized by cooling within a range of ± 1.0.

[0007]

When the thick steel plate before finish rolling is cooled, the plate thickness is large, the temperature gradient in the plate thickness direction during cooling is large, and the surface temperature of the thick steel plate is in the low temperature range below the transition boiling range. Along with this, the cooling capacity of the plate water is increased, and in order to correct it, the ratio of lower water to upper water (lower / upper) is increased. The tendency becomes greater as the plate thickness during cooling increases. Therefore, Table 1
And as shown in Fig. 1, the ratio of sewage volume to (plate thickness (m
By changing the range of m) / 30) ± 1.0,
It has an excellent effect that it enables a rolling pass immediately after that and surely prevents the warp.

[0008]

[Table 1]

[0009]

[Example] The rolling situation of control rolling will be disclosed as an example. Slab dimensions (thickness 211mm, width 1770mm,
Product length (thickness 23.5 mm, width 26)
In rolling of 80 mm and length of 29000 mm, the rolling condition is regulated as a CR condition with a transfer thickness of 54 mm and a rolling temperature of 890 ° C. or less. Table 2 shows the rolling pass schedule of this CR rolled material. FIG. 2 shows the temperature transition during rolling when water cooling is not performed in this rolling schedule. Air cooling is performed for 260 seconds at a plate thickness of 54 mm after 10 passes. Next, FIG. 3 shows the temperature transition when the thick steel plate after 10 passes is cooled at a water / water ratio of 2.5 by the cooling method of the present invention.

As can be seen from FIG. 3, when the temperature waiting time up to the CR start temperature is cooled and reheated at a specific thickness as compared with 260 seconds in the case of air cooling by the conventional method, 160
It is clear that it is greatly shortened to seconds. No warpage occurred after 11 passes.

[0011]

[Table 2]

[0012]

As described above, when the thick steel sheet before finish rolling is cooled by the cooling method of the present invention, the warpage in the subsequent finish rolling is changed by largely changing the ratio of water and sewage according to the plate thickness. It has an excellent effect of preventing

[Brief description of drawings]

FIG. 1 shows the relationship between the plate thickness during cooling and the sewage ratio.

FIG. 2 shows a temperature transition of a steel sheet during rolling.

FIG. 3 shows the temperature transition of the steel sheet when waiting for the CR temperature.

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[Procedure amendment]

[Submission date] July 9, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

[0008]

[Table 1]

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichiro Takeshita No. 1 Nishinosu, Oita City, Oita Prefecture New Nippon Steel Co., Ltd. Oita Works

Claims (1)

[Claims] 1. When cooling the upper surface of a thick steel plate having a plate thickness of 40 mm or more before finish rolling with a laminar flow and spraying the lower surface with a spray, the water content ratio (lower / upper) of the upper and lower surfaces is changed according to the plate thickness. (Mm) / 30) A method for cooling thick steel plates, characterized by cooling within a range of ± 1.0.