JP2001018039A - Cooling method for continuous cast slab - Google Patents

Abstract

(57) [Summary] The present invention adjusts the amount of cooling water in each zone in a wider range than before without changing existing nozzles when performing secondary cooling of continuous cast slab by water spray. It is an object of the present invention to provide a method of cooling a continuous cast slab that is possible. A slab that has escaped from a water-cooled mold of a continuous casting machine is supported by a support roll, passes through a secondary cooling zone composed of a group of nozzles divided into a plurality of zones, and is cooled by spraying cooling water. The spraying of the cooling water and the stopping of the spraying were repeated at regular intervals.

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 continuous cast slab, and more particularly to a method for continuously casting a molten steel in a continuous casting machine for molten steel. This is a technique for smooth and good secondary cooling.

[0002]

2. Description of the Related Art As shown in FIGS. 1 and 2, a continuous casting method for producing steel slabs (slabs, blooms, etc.) is as follows: a molten steel 1 is poured into a water-cooled mold 4 via a ladle 2 and a tundish 3. The semi-solid 5 whose surface is solidified but the inside is still in a molten state is cooled by applying water 7 while being transported to the downstream side while being supported by a plurality of support rolls 6 (secondary cooling and Good), and the whole is completely solidified, and after solidification, the shape of the slab 9 is corrected by the straightening machine 8. In addition, the casting machine 10 for performing such continuous casting includes a vertical mold for moving the slab 9 coming out of the mold 4 vertically, a curved mold for moving while bending (see FIG. 1), There is a vertical bending type (see FIG. 2) that bends the direction from the center. As shown in FIG. 3, the apparatus used for the secondary cooling is composed of a nozzle for spraying water directly on the slab 9 and a nozzle for spraying water on the surface of the support roll 6 supporting the slab 9. A plurality of such nozzles constitute one zone, and some of the nozzles (No. 1 and N in FIG. 2) are used.
o. 2 zones) at both ends in the slab width direction and along the running direction.

[0003] The secondary cooling by the water spray is performed by a slab 9
It is extremely important from the viewpoint of controlling the solidification structure and preventing cracking, and various techniques have been studied and developed from the viewpoint of both hardware and software.

In the current secondary cooling method, a constant amount of cooling water to be sprayed in each zone is determined in advance in accordance with the steel type and size of the cast slab, and several patterns relating to the amount of water are prepared. This is done by selecting an appropriate pattern for the slab. This method
There is an advantage that cooling can be performed by a relatively simple operation. However, in some cases, it is not possible to meet the recent demands for slab quality. In other words, even if it is necessary to cool the slab more strictly, the ability of the installed nozzles (water volume, spray pattern, etc.) is limited, so it is not possible to reduce or increase the cooling as desired. A case has arisen. In particular, when casting a newly developed steel type, the pattern of the similar steel type is adopted, and appropriate secondary cooling is sought by trial and error, but it takes considerable time to obtain satisfactory results. . Furthermore, when the secondary cooling is not performed properly and a part of the slab is partially supercooled, when the shape of the slab 9 is corrected on the downstream side, surface cracks of the slab 9 may occur. The problem of arising remains.

[0005]

SUMMARY OF THE INVENTION In view of the foregoing, the present invention has been made to solve the problem that when performing secondary cooling of a continuous cast slab by water spray, the amount of cooling water in each zone can be changed without changing an existing nozzle. It is an object of the present invention to provide a method of cooling a continuously cast slab that can be adjusted over a wider range.

[0006]

Means for Solving the Problems The inventor has conducted intensive studies to achieve the above object and has embodied the results in the present invention.

That is, according to the present invention, a slab that has escaped from a water-cooled mold of a continuous casting machine is supported by a support roll, passed through a secondary cooling zone composed of a group of nozzles divided into a plurality of zones, and sprayed with cooling water. A method of cooling a continuous cast slab, wherein the cooling water spraying and the spraying stop are repeated at regular time intervals during cooling.

[0008] The present invention is also a method of cooling a continuous cast slab, wherein the above-mentioned repetition at regular intervals is individually performed in each of the above zones.

Further, the present invention is also a method for cooling a continuous cast slab, wherein the continuous caster is of a curved type or a vertical bent type, and the repetition is performed at regular intervals only inside the radius.

According to the present invention, the amount of cooling water (cooling stop time) applied to the slab can be adjusted in a wide range, so that the cooling rate can be gradually changed depending on the position of the slab without changing the performance (specification) of the nozzle. Alternatively, strong cooling becomes free. as a result,
The slab quality (segregation, surface cracking, etc.) becomes more stable than before. Further, if the present invention is carried out only on the inside of the radius of the continuous casting machine, it becomes possible to prevent surface cracks at the time of correcting the shape of the slab.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

First, according to the present invention, as shown in FIGS. 1 and 2, a large number of nozzles 11 are arranged along the width direction of a slab 9.
The cooling water 7 is sprayed onto the slab at regular time intervals, or the spraying is stopped. That is, the spraying of the cooling water 7 is turned on, the stop is turned off, and the cooling water 7 is turned on-off (see FIG. 4A). As a result, the amount of water applied to the slab 9 is reduced, so that the amount of water to be sprayed on the slab 9 can be changed widely by setting various intervals for the predetermined time. In this case, it is important to set a certain time interval so that the support roll 6 supporting the slab does not break. This fixed time has many influencing factors such as the size of the slab 9, the type of steel, the traveling speed, and the like, and it is difficult to determine the given time by the casting machine 10 in a general manner. Therefore, the inventor conducted a test in which the certain time was changed variously, and
It has been found that it is preferable to carry out in the range of 10 to 10 seconds.
If the time exceeds 10 seconds, the cooling of the roll was insufficient, and there was a risk of breakage. If the time is shorter than 1 second, the effect of stopping the cooling is small, and the cooling water switching valve is damaged.

Further, it is preferable that the cooling water amount On-Off is performed for each zone of the secondary cooling zone, for example, as shown in FIG. This is because the number of types of cooling patterns increases, and appropriate measures can be taken to change the steel type and size of the slab to be cooled.

Further, according to the present invention, when the continuous casting machine is of a curved type or a vertical bent type as shown in FIGS.
The group of nozzles for performing -Off is preferably limited to those arranged inside the radius of the continuous casting machine. Thereby, the supercooled portion generated on the radius side of the slab 9 is reduced, the generation of cracks is suppressed, and the surface cracks at the time of shape correction can be prevented.

[0015]

EXAMPLE A molten steel 1 was cast using a curved continuous caster having a mold cross section of 400 × 560 mm (see FIG. 1), and a steel slab 9 was produced continuously. At that time, the casting speed of the molten steel was 0.5 m / min. The molten steel 1 to be cast is a type having a high surface sensitivity when it comes to a steel material.
0% by weight, 0.025% by weight of Al, 0.030% of Nb
Those containing weight% were selected. The nozzles 11 for spraying the cooling water were arranged in two zones, each having 10 nozzles as one zone on both sides of the running line of the slab 9. Each of the nozzles is porous so that water 7 can be uniformly sprayed in the thickness direction of the slab 9. The amount of water sprayed on the slab 9 is usually the same as that of the No. 1 nozzle 11 arranged on both sides of the slab 9. No. 1 zone is 5 liters / min. Two zones were 5 liters / minute.

Table 1 shows the results obtained in such a cooling condition. In addition, in order to confirm the effect of the present invention, Table 1 also shows the results of a conventional cooling method (without on-off) as a comparative example. From Table 1, it is clear that in the practice of the present invention, no surface cracks occur in the slab. Further, when the cross section of the slab was examined, segregation was significantly reduced as compared with the conventional one. The segregation was determined in advance on a macro cross-sectional photograph of a standard sample exhibiting various segregation states in five stages of criteria (4 for large segregation and 0 for no segregation).
) Was prepared, and the macro section of the slab obtained in the practice of the present invention was evaluated in comparison with the photograph. Further, the casting machine 10
When On-Off is performed only on the round side of
Was maintained higher than the opposite side. As a result, no crack was generated at the time of correcting the shape of the cast slab at all.

[0017]

[Table 1]

[0018]

As described above, according to the present invention, the amount of cooling water (cooling stop time) applied to a slab can be adjusted in a wide range, and the casting water can be cast without changing the capability (specification) of the existing nozzle. Slow cooling or strong cooling became possible depending on the position of the piece. As a result, the quality of the slab (segregation, surface cracks, etc.) becomes more stable than before. Further, when the present invention was implemented only on the inside of the radius of the continuous casting machine, the surface cracks at the time of correcting the shape of the slab could be completely prevented.

[Brief description of the drawings]

FIG. 1 is a side view showing a general curved continuous casting machine.

FIG. 2 is a side view showing a general vertical bending type continuous casting machine.

FIG. 3 is a diagram illustrating a nozzle arrangement of a continuous casting machine.

FIG. 4 is a diagram for explaining the On-Off state of the cooling water. 1 and No. 1 (B) shows an example in which the value of the fixed time is the same in the two zones, and (b) is different.

[Explanation of symbols]

 Reference Signs List 1 molten steel 2 ladle 3 tin tissue 4 water-cooled mold (mold) 5 semi-solid 6 support roll (roll) 7 cooling water (water) 8 straightener 9 cast piece 10 continuous caster

Claims (3)

[Claims] 1. A method for cooling a slab that has escaped from a water-cooled mold of a continuous casting machine by passing it through a secondary cooling zone composed of a group of nozzles divided into a plurality of zones supported by a support roll and spraying cooling water. A method of cooling a continuous cast slab, wherein the spraying of the cooling water and the stopping of the spraying are repeated at regular intervals. 2. The method for cooling a continuous cast slab according to claim 1, wherein the repetition at regular intervals is performed individually in each of the zones. 3. The method for cooling a continuous cast slab according to claim 1, wherein the continuous caster is a curved type or a vertical bent type, and the repetition is performed at regular intervals only inside the radius.