JP2004344893A - Slab cooling method in continuous steel casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method useful for preventing a slab from being bent when cooling the slab after steel is continuously cast and cut to a predetermined length. <P>SOLUTION: When cooling a slab after steel is continuously cast and cut to a predetermined length, the operation is performed so that the inequality (1) (C1-C2)/C1<0.15 is satisfied, where C1 and C2 (°C/min: C1≥C2) denote the mean cooling rate at surfaces facing each other of the slab within the range of the slab temperature of 800 to 500°C, respectively. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２２】
これらの結果を、鋳片上面における平均冷却速度Ｃ１、鋳片下面における平均冷却速度Ｃ２、および前記（１）式の左辺の値［（Ｃ１−Ｃ２）／Ｃ１］と共に、下記表２に示す。また、これらの結果に基づいて、平均冷却速度Ｃ１、Ｃ２の関係が鋳片曲がり発生に与える影響を図１に、（Ｃ１−Ｃ２）／Ｃ１と曲がり量の関係を図２に夫々示す。
【００２３】
【表２】

【００２４】
これらの結果から明らかなように、上記（１）式を満足することによって、ビレット鋳片における曲がりの発生を効果的に防止できることが分かる。
【００２５】
【発明の効果】
本発明は以上の様に構成されており、鋼を連続鋳造して所定の長さに切断した後のビレット鋳片を冷却するに際して、ビレット鋳片に曲がりが発生しないための有用な方法が実現できた。
【図面の簡単な説明】
【図１】鋳片各面における平均冷却速度Ｃ１、Ｃ２の関係がビレット鋳片曲がり発生に与える影響を示すグラフである。
【図２】（Ｃ１−Ｃ２）／Ｃ１と曲がり量の関係を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for cooling a billet slab after continuously casting steel and cutting the steel to a predetermined length, and in particular, to prevent bending of the billet slab during this cooling. And cooling methods for the same.
[0002]
[Prior art]
The continuous casting method of steel is a manufacturing method in which molten steel is solidified through a mold (primary cooling), further cooled by spraying or air mist (secondary cooling), and the slab is continuously drawn and cut to a predetermined length. is there. Then, the cut slab is further cooled (tertiary cooled) before being conveyed to the subsequent slab rolling.
[0003]
In this tertiary cooling, cooling or forced cooling is performed. However, when cooling is performed, there is a problem that a large space is required and it is not practical. For this reason, forced cooling is generally performed in the tertiary cooling. For this forced cooling, (1) a method of immersing a slab in cooling water, (2) a method of spraying cooling water on the slab, and the like are known. Among these methods, from the viewpoint of uniformly cooling the slab, the above method (1) is superior, but from the viewpoint of setting appropriate cooling conditions according to the steel type of the slab. If so, the above method (2) is said to be excellent.
[0004]
In adopting the cooling method of (2), the cooling water is controlled so that the same amount of cooling water is sprayed on each surface (for example, the upper surface and the lower surface) of the cast slab as much as possible. Differences tend to occur. For example, cooling water easily accumulates on the upper surface of the slab and cooling is promoted, but cooling water flows out on the lower surface of the slab and cooling is hardly promoted. Such non-uniform cooling causes the slab to bend. In particular, in the case of low-alloy steel or billet cast pieces having a small cross-sectional shape (each piece is about 150 mm), it is said that such a bend easily occurs due to a high heat removal rate.
[0005]
When such slab bending occurs, there is a problem that the slab is not transported smoothly. More specifically, the slab can be passed through facilities such as a maintenance line and a sizing process performed subsequent to continuous casting, which hinders continuous operation. Further, when the bent slabs are stacked, the bending is corrected and the slab is cracked.
[0006]
For these reasons, various cooling methods for preventing bending due to a difference in cooling have been proposed. In connection with such a technique, a steel slab having a high temperature of about 700 to 1000 ° C. is sprinkled with water from a number of cooling nozzles, and in cooling the steel slab, the sprinkling is returned to a substantially uniform temperature. A method has been proposed in which a steel slab is intermittently repeated until the steel slab is cooled to 130 to 200 ° C. in a cycle such as cooling with water after heating (for example, see Patent Document 1).
[0007]
Although this technique is intended to prevent the occurrence of bending in a rolled billet, it is an effective method for preventing bending due to a difference in cooling. However, this method requires strict control of cooling conditions, and has a problem that it is difficult to apply as a method of performing tertiary cooling in continuous casting.
[0008]
In addition, as a cooling method after the slab rolling process, spray cooling is performed by immersing almost the lower half of the hot steel slab in water while cooling while simultaneously exposing the remaining upper half on the water surface, and always performing upper and lower surfaces. There is also proposed a method of controlling a temperature difference within 100 ° C. (for example, Patent Document 2).
[0009]
This technique uses the above methods (1) and (2) in combination. However, even if such a technique is applied, uniform cooling of the slab is not achieved, and from the viewpoint of preventing the slab from bending, Still insufficient.
[0010]
[Patent Document 1]
JP, 48-96410, A Patent, etc. [Patent Document 2]
Japanese Patent Publication No. 52-16445 Patent claims etc.
[Problems to be solved by the invention]
The present invention has been made under such a circumstance, and an object of the present invention is to prevent bending of a billet slab when cooling a billet slab after continuously casting steel and cutting the steel to a predetermined length. It is to provide a useful method for.
[0012]
[Means for solving the problem]
The method of the present invention, which has achieved the above object, is to cool a billet slab after continuously casting steel and cutting the steel to a predetermined length. When the average cooling rates on the opposing surfaces of the pieces are C1 and C2 (° C./min: C1 ≧ C2), these have a gist in that they operate so as to satisfy the relationship of the following formula (1). Things.
[0013]
(C1-C2) / C1 <0.15５ (1)
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have studied from various angles a useful method for cooling a billet slab while preventing bending thereof. As a result, if the average cooling rate on the opposite surface of the slab satisfies the predetermined relation [the relation of the above formula (1)], uniform cooling of the slab is achieved and the billet slab is bent. The present invention was completed.
[0015]
In the present invention, the “opposite surface” typically has a relationship between the upper surface and the lower surface, but is not limited to such a state, and the effects of the present invention can be achieved by appropriately controlling the cooling rates on both side surfaces. You. It is also possible to use the cooling rate control for the upper and lower surfaces and both sides of the slab together. In short, it suffices to control the amount of cooling water and the like so that the average cooling rate on the “opposite surface” satisfies the relationship of the above equation (1). Thereby, the occurrence of bending of the billet slab can be suppressed.
[0016]
The reason why the average cooling rates C1 and C2 are controlled is that the slab temperature needs to be in a temperature range of 800 to 500 ° C., because this is a temperature range where unevenness of cooling is likely to be manifested as bending. That is, even if the average cooling rate is controlled in a state where the slab temperature exceeds 800 ° C. or becomes lower than 500 ° C., it is not so effectively reflected in the prevention of bending.
[0017]
Specific means for controlling the average cooling rates C1 and C2 so as to satisfy the relationship of the expression (1) include (1) optimizing the balance of the amount of cooling water on the opposing surfaces, and (2) spraying the cooling water. In this case, the average cooling rate on each surface can be made uniform by optimizing the arrangement of the nozzles for (3) rotating the slab. However, when the upper and lower surfaces of the slab are selected as opposing surfaces, the average cooling rate on the upper surface is not always higher than the cooling speed on the lower surface. Of course, the control may be performed so that
[0018]
The type of steel material targeted in the present invention is not limited as long as it is a steel material manufactured as a continuous cast piece, and can be applied to various steel types such as high alloy steel, low alloy steel, and low carbon steel. However, in order to more effectively exert the effects of the present invention, it is preferable that the alloy be a low alloy steel in which billet slab bending is most likely to occur. In the present invention, the specific control range of the average cooling rates C1 and C2 varies depending on the steel type to be used, and is not particularly limited. For example, in the case of the low alloy steel, the control range is 20 to 80 ° C. / Min.
[0019]
Hereinafter, the operation and effect of the present invention will be more specifically described with reference to examples.However, the following examples are not intended to limit the present invention, and it is possible to appropriately change the design within a range applied to the purpose described above and below. Both are included in the technical scope of the present invention.
[0020]
【Example】
Example 1
A billet slab [length: 8000, length: 155, width: 155 (mm)] was manufactured from molten steel having a chemical composition shown in Table 1 by a continuous casting method, and the obtained billet slab was cooled under various cooling conditions. (Table 2 below) and the amount of bending of each billet slab was investigated. The cooling conditions at this time were changed by controlling the amount of spray water. The amount of bending was measured by measuring the bending height h of each slab (the height to the lower surface when the slab was assumed to be placed on a horizontal plane), and depending on whether or not the value became 50 mm or more, the bending condition was determined. Was evaluated ("x" for 50 mm or more, "O" for less than 50 mm).
[0021]
[Table 1]

[0022]
The results are shown in Table 2 below together with the average cooling rate C1 on the slab upper surface, the average cooling rate C2 on the slab lower surface, and the value [(C1-C2) / C1] on the left side of the above equation (1). Also, based on these results, FIG. 1 shows the effect of the relationship between the average cooling rates C1 and C2 on the occurrence of slab bending, and FIG. 2 shows the relationship between (C1−C2) / C1 and the amount of bending.
[0023]
[Table 2]

[0024]
As is clear from these results, it can be seen that the occurrence of bending in the billet slab can be effectively prevented by satisfying the expression (1).
[0025]
【The invention's effect】
The present invention is configured as described above, and realizes a useful method for preventing bending of billet slab when cooling billet slab after continuous casting of steel and cutting to a predetermined length. did it.
[Brief description of the drawings]
FIG. 1 is a graph showing the influence of the relationship between average cooling rates C1 and C2 on each side of a slab on the occurrence of billet slab bending.
FIG. 2 is a graph showing a relationship between (C1−C2) / C1 and a bending amount.

Claims (1)

In cooling the billet slab after continuous casting of steel and cutting to a predetermined length, the average cooling rates on the opposite surfaces of the slab in the range of 800 to 500 ° C. of the slab are C1 and C2, respectively. (C / min: C1 ≧ C2), a method for cooling a slab in continuous casting of steel, wherein the operation is performed so that these satisfy the relationship of the following formula (1).
(C1-C2) / C1 <0.15５ (1)

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