JPH08206794A - Continuous casting method of slab of large section and continuous casting equipment - Google Patents

Abstract

PURPOSE: To prevent the generation of surface flaws due to the inclination by arranging the closest part of the molten steel to be discharged in the direction approximately parallel to a pair of inner wall surfaces opposite to each other of a mold so as to be within the prescribed range from the inner wall surfaces. CONSTITUTION: The closest part of the molten steel indicated by the arrows C, D, E, F to be discharged from two sets of discharge ports (3c, 3d), (3e, 3f) to a pair of inner wall surfaces 1a, 1b respectively is arranged to be within the range of 50-150mm from the inner wall surfaces 1a, 1b respectively. When the position of the closest part of the molten steel is within <50mm, the growth of the solidified shell is remarkably delayed, and adverse effects such as the breakout are generated. When the position of the closest part exceeds 150mm, the reducing effect of the inclination is lost even when less molten steel of high temperature is fed to the contact part of the meniscus part. Generation of surface flaws can be prevented by a simple device in the continuous casting of the slab of large section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a thickness of 600 to 1, for example.
TECHNICAL FIELD The present invention relates to a method for continuously casting a large cross-section slab having a cross-sectional size of 000 mm and a width of 700 to 3000 mm, and an apparatus therefor, and a technique for continuously casting a large-section slab having excellent surface quality. It is about.

[0002]

2. Description of the Related Art In casting a large cross-section slab as described above, continuous casting has previously been difficult due to dimensional constraints and the like. It is generally carried out, and various techniques have been proposed from such a viewpoint.

On the other hand, the widespread use of continuous casting operations in the steel manufacturing industry has greatly contributed to cost rationalization in terms of yield improvement, energy saving and labor saving. For these reasons, in recent years, it has been attempted to apply the continuous casting method even when casting a large-section slab as described above.

In the production of such a large-section slab by the continuous casting method, the casting speed is set to be much slower than in the case of producing a normal slab from the viewpoint of preventing bulging of the slab. Is common. For example, in the case of a large-section slab having a cross-sectional size of 700 mm × 1400 mm, the casting speed is about 0.1 m / min.

[0005]

However, in the low-speed casting as described above, there is a phenomenon called so-called collapse of the solidified shell, in which the solidified shell collapses inward from the surface of the slab at the contact portion between the molten steel meniscus and the mold. There is a problem of manifestation. When this phenomenon becomes apparent,
If the surface of the slab becomes uneven, and if the degree of this unevenness becomes severe, it will cause surface defects during forging and rolling, and will impair the quality of the product.

In the present continuous casting method, good lubricity between the cast piece and the mold is also an important requirement. As a means for achieving the lubricity, a lubricant called mold flux is used for the cast piece. The casting is performed while the molten metal is present between the mold and the mold. However, if the melting of the mold flux is insufficient, the lubricity between the slab and the mold is not maintained well, and sticking occurs between the slab and the solidified shell on the surface of the slab and the so-called breakout occurs. There's a problem. As a technique for solving such a problem, a technique such as Japanese Patent Laid-Open No. 57-109952 has been proposed. In this technique, the electrode is immersed in the flux layer formed on the molten steel surface in the mold, the flux is melted by the resistance heat associated with energization, and a molten flux layer having a predetermined thickness is secured on the molten steel surface. is there. According to this technique, from the viewpoint of preventing the occurrence of breakout due to insufficient melting of the mold flux, it is considered that a temporary effect can be obtained. It is also said that this technique achieves the effect of preventing surface defects due to unmelted flux.

However, even this technique is still insufficient from the viewpoint of preventing the occurrence of surface defects due to a phenomenon called collapse of the solidified shell, and it is desired to establish a technique for eliminating such inconvenience. It is the actual situation.

The present invention has been made in order to solve the technical problems in the prior art, and the purpose thereof is a phenomenon called collapse of a solidified shell when continuously casting a large-section slab (hereinafter referred to as "falling down"). A method capable of effectively preventing the occurrence of surface flaws caused by the "falling phenomenon") and an apparatus for carrying out this method with a simpler configuration.

[0009]

According to the method of the present invention which has achieved the above object, molten steel is supplied to a rectangular mold whose upper and lower sides are opened through a discharge port of a dipping nozzle, and a slab is continuously cast from a lower part of the mold. Of the molten steel discharged from the discharge port so as to be discharged in a direction substantially parallel to a pair of inner wall surfaces of the mold facing each other when the rectangular large-section cast slab is cast by drawing Is a continuous casting method of a large-section cast slab, which is characterized in that it is arranged and operated so as to be within a range of 50 to 150 mm from each of the set of inner wall surfaces of the mold.

On the other hand, the apparatus of the present invention that achieves the above object is to supply molten steel to a rectangular mold whose upper and lower sides are opened through the discharge port of a dipping nozzle, and continuously pull out the slab from the lower part of the mold. A device for casting a rectangular large-section cast slab, which is the closest to molten steel discharged from the discharge port so as to be discharged in a direction substantially parallel to a pair of inner wall surfaces facing each other of the mold. Part is 50 to 150 from the inner wall surface of the mold.
It is a continuous casting apparatus for large-section cast slabs, which is characterized in that it is arranged so as to be within the range of mm. Further, as a more specific configuration of this continuous casting apparatus, as will be described later, one in which the discharge ports are formed in pairs from each of the inner wall surfaces of the set can be mentioned.

[0011]

First, the present inventors examined the cause of the collapse phenomenon in the prior art. Figure 2
FIG. 1 is a plan view showing the vicinity of a mold of a conventional casting apparatus, which is shown in FIG.
Is a rectangular mold, 2 is a dipping nozzle, 3a and 3b are nozzle outlets, respectively. In the conventional casting device, as shown in FIG.
The submerged nozzle 2 is arranged substantially in the center of the rectangular mold 1, and the molten steel from the discharge ports 3a, 3b is associated with it by arrows A, B so as to be substantially parallel to the pair of facing inner wall surfaces 1a, 1b. Is discharged as follows. The inner wall surfaces 1a and 1b are generally inner wall surfaces on the long side of the mold. When continuously casting a large-section slab with such a configuration, the discharge port 3
The molten steel discharged from a and 3b is the inner wall surface 1 of the pair.
Another pair of inner wall surfaces 1c and 1d facing each other different from a and 1b
After contact with the inner wall surfaces 1a, 1b, the molten steel is cooled until it moves to the inner wall surfaces 1a and 1b, and the molten steel sequentially supplied reaches a contact portion with the mold. It will be formed into meat and this inner wall surface 1
It was considered that the above-mentioned collapse phenomenon is likely to occur in a and 1b. Further, especially during rolling, since the pair of inner wall surfaces 1a and 1b on the long side generally serves as a rolling surface, the quality of the surface of the slab on this surface side becomes a problem. However, even if the solidified shell is too thin, breakout easily occurs.

In order to reduce the above-mentioned collapse phenomenon,
In particular, it is necessary to raise the molten steel temperature of the meniscus on the inner wall surfaces 1a, 1b on the long side of the mold, and it is conceivable to raise the pouring temperature as a means of increasing the temperature. However, raising the pouring temperature more than necessary causes segregation. However, there is a limit because the quality of the slab such as increase in the quality of the slab is deteriorated. Therefore, the present inventors have taken these points into consideration, and examined from various angles a specific configuration for preventing the collapse phenomenon. As a result, if the operation is performed by appropriately setting the distance between the closest portion of the molten steel discharged from the discharge port and the inner wall surface of the mold, the inner wall surface 1a, without increasing the casting temperature more than necessary, It has been found that a molten steel having a relatively high temperature can be supplied to the meniscus portion on the 1b side, and a large-section slab having excellent surface quality can be produced while effectively preventing the occurrence of the collapse phenomenon, and the present invention completed.

FIG. 1 is a plan view showing the vicinity of a mold of an example of the constitution of the casting apparatus of the present invention, the basic constitution thereof corresponds to the constitution shown in FIG. 1, and the same reference numerals are used for the corresponding portions. The reference numeral is attached. In this device, two pairs of discharge ports (3c, 3d) and (3e, 3f) are connected to each pair of discharge ports (3
c, 3d), (3e, 3f) are the inner wall surfaces 1a,
One pair is formed for each of 1b (total of four) and is discharged from each pair of discharge ports (3c, 3d), (3e, 3f) (arrows C, D, E, F) closest to the molten steel. The parts are arranged so as to be within a range of 100 mm from each of the inner wall surfaces 1a and 1b. When a large-section slab is continuously cast by operating with such an apparatus configuration, high-temperature molten steel is melted by the set of inner wall surfaces 1a,
1b, the occurrence of the collapse phenomenon is effectively prevented. Moreover, the device shown in FIG. 1 has a relatively simple structure.

In the present invention, as described above, the discharge port (3
c, 3d), (3e, 3f), the closest portion of the molten steel discharged from each must be arranged to be within a range of 50 to 150 mm from each of the inner wall surfaces 1a, 1b of the rectangular mold 1. However, the reason for this is as follows. That is, the position of the portion closest to the molten steel is the inner wall surface 1a or 1b of the rectangular mold 1.
If it is less than 50 mm, the growth of the solidified shell is remarkably delayed, and the above-mentioned problems such as breakout occur. Further, when the position of the closest portion of the molten steel exceeds 150 mm from the inner wall surface 1a or 1b of the rectangular mold 1, the supply of the high temperature molten steel to the contact portion of the meniscus portion becomes small, and the effect of reducing the collapse phenomenon cannot be exhibited.

The present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the present invention, and any modification of the design of the present invention can be made without departing from the spirit of the preceding and the following. It is included in the technical scope.

[0016]

EXAMPLE The present invention was carried out by using the casting apparatus having the structure shown in FIG. 1, a large-section cast slab having a section of 700 mm × 1400 mm was manufactured, and the occurrence of surface defects was investigated. At this time, as a comparative example, the state of occurrence of surface defects in the slab having the same cross-sectional shape manufactured using the conventional casting apparatus shown in FIG. 1 was also investigated. Regarding the occurrence of surface defects,
The height of irregularities and the number of surface defects were measured.

The results are shown in FIGS. 3 and 4, respectively.
The number of surface defects generated was expressed as an index when the number of surface defects generated in the conventional method was 100 after the number of surface defects generated was measured after rolling the above slab at a rolling reduction ratio of 3. As is clear from these results, the method of the present invention has smaller irregularities on the surface of the slab than the conventional method, and the number of surface defects after rolling is remarkably improved.

[0018]

EFFECT OF THE INVENTION The present invention is configured as described above, and when continuously casting a large-section slab, it is possible to effectively prevent the occurrence of surface flaws due to the phenomenon of collapse. Moreover, it was possible to achieve it with a simpler device configuration.

[Brief description of drawings]

FIG. 1 is a plan view showing the vicinity of a mold of a structural example of a casting apparatus for carrying out the present invention.

FIG. 2 is a plan view showing the vicinity of a mold portion of a conventional casting device.

FIG. 3 is a bar graph showing the height of unevenness of a slab by comparing the method of the present invention with the conventional method.

FIG. 4 is a bar graph showing a surface flaw generation index after rolling, comparing the method of the present invention with the conventional method.

[Explanation of symbols]

 1 Rectangular mold 1a-1d Inner wall surface 2 Immersion nozzle 3a-3f Discharge port

Claims (3)

[Claims] 1. When a molten steel is supplied to a rectangular mold whose upper and lower sides are opened through a discharge port of a dipping nozzle, and a slab is continuously drawn from the lower part of the mold to cast a rectangular large-section slab. The closest portion of the molten steel discharged from the discharge port so as to be discharged in a direction substantially parallel to the pair of inner wall surfaces of the mold facing each other is 50 from each of the pair of inner wall surfaces of the mold. A continuous casting method of a large-section cast slab, which is arranged and operated so as to be within a range of up to 150 mm. 2. In order to cast a rectangular large-section slab by continuously supplying molten steel to a rectangular mold whose upper and lower sides are opened through a discharge port of a dipping nozzle and continuously withdrawing the slab from the lower part of the mold. In the apparatus, the closest portion of the molten steel discharged from the discharge port so that the molten steel is discharged in a direction substantially parallel to a pair of inner wall surfaces of the mold facing each other from each of the inner wall surfaces of the mold. A continuous casting device for a large-section cast slab, which is arranged so as to be within a range of 50 to 150 mm. 3. The continuous casting apparatus according to claim 2, wherein the discharge ports are formed in pairs on the inner wall surfaces of the set.