JPH08112654A - Tundish for continuously casting steel - Google Patents

Abstract

PURPOSE: To effectively separate fine inclusions in molten steel by forming plural annular recessed parts for absorbing inclusions on the inner wall of a molten steel passing hole by generating eddy flow in the molten steel. CONSTITUTION: The molten steel 2 in a ladle 1 is poured into a molten steel receiving chamber 9 in a tundish 3 from a nozzle 5 and allowed to flow into a molten steel pouring chamber 10 through many molten steel passing holes 7 formed with plural annular recessed parts 6 on the hole wall. When the molten steel passes through the molten steel passing holes 7, the eddy flow is generated in the molten steel 2 flow by action of the annular recessed parts 6 and the fine inclusions in the molten steel are allowed to flow into the annular recessed parts 6 to sufficiently circulate the parts 6, thereafter the inclusions are absorbed into the corner part and separated from the molten steel 2. In this result, the molten steel 2 is cleaned and allowed to flow into the molten steel pouring chamber 10 and continuously supplied into a mold 11 from a tundish nozzle 3a through a sliding nozzle SN. The molten steel 2 supplied into the mold is cooled in the mold 11 to formed the solidified shell 14s and drawn out as a cast slab 14 by many supporting rolls 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tundish for continuous casting of steel having a structure for effectively separating inclusions in molten steel.

[0002]

2. Description of the Related Art Generally, in a continuous casting machine used for continuous casting of steel, as conceptually shown in FIG.
The molten steel s is received by the tundish b from the ladle a, poured from the tundish nozzle b into the water-cooled copper mold d through the sliding nozzle n, and cooled by this mold to produce a solidified shell ss, and the obtained casting is obtained. It has a structure in which one piece sc is supported and carried out through a large number of support rolls r arranged below the mold. In the tundish b used here, inclusions are separated and removed so that the inclusions that impair the quality of the slab are not mixed in the molten steel injected into the mold.

For example, in Japanese Patent Laid-Open No. 58-212848, a weir on the molten steel inlet side is provided in the tundish in which the upper end projects above the molten steel surface and a gap is provided between the lower end and the bottom wall so that the molten steel can pass therethrough. A plate and a weir plate on the molten steel outlet side whose upper end is below the molten steel surface are divided into a molten steel inlet side tank and a molten steel outlet side tank, and molten steel from the ladle is
It is performed that the inclusions are separated by flowing from the lower end of the weir plate on the molten steel inlet side to the upper end of the weir plate on the molten steel outlet side to inject the cleaned molten steel into the mold. This example is an effective means for inclusions having a large grain size that are easily separated and floated, but is not necessarily an effective means for fine inclusions mixed in molten steel.

On the other hand, as a means for separating such fine inclusions, there is a method in which Ar gas is blown to generate bubbles, and the inclusions are attached to the bubbles, and then floating separation is performed. However, in this method, since it is difficult to generate a large amount of fine bubbles, the molten steel and the bubbles are not sufficiently contacted with each other, and the fine inclusions cannot be sufficiently separated.

Another method is to pass molten steel through a filter made of breathable refractory and separate inclusions with this filter. However, with this method, the pressure loss is large, it is not possible to secure a sufficient injection amount for the mold, the filter is likely to be clogged, and it is necessary to frequently replace the filter, which reduces productivity and increases the filter cost. To do.

As described above, in the conventional example, it is the actual situation that no method capable of sufficiently evaluating inclusions has been found.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a tundish for continuous casting of steel having a structure capable of effectively separating fine inclusions in molten steel. The purpose is.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a partition wall having a plurality of holes through which molten steel can pass is disposed, and a molten steel receiving chamber from a ladle and a bottom wall are filled with molten steel in a mold. In a tundish having a molten steel injection chamber provided with a nozzle, a plurality of annular recesses (projections) are formed on the inner wall of the molten steel passage hole to generate swirl in the molten steel to adsorb inclusions. Is a tundish for continuous casting of steel.

[0009]

In the tundish of the present invention, a partition wall having a plurality of holes through which molten steel can pass is arranged to partition the inside of the tundish into a molten steel receiving chamber and a molten steel pouring chamber, and the molten steel from the ladle is molten steel. Receiving in the receiving room, annular concave (convex) on the hole wall
The molten steel is passed through the molten steel passage hole formed in the portion to flow into the molten steel injection chamber.

According to the present invention, due to the action of the annular concave (convex) portion formed in the hole wall of the molten steel passage hole, a swirl is generated in the molten steel flow passing therethrough to increase the frequency of contact between the hole wall and fine inclusions. be able to. As a result, adsorption of inclusions on the wall of the hole is promoted, and the molten steel can be cleaned and guided to the molten steel pouring chamber. Therefore, the quality of the slab obtained after pouring into the mold and cooling can be improved.

In the present invention, the shape of the molten steel passage hole of the partition wall is not particularly limited, but is circular in view of the ease of hole formation. The diameter d of the through hole is preferably small from the viewpoint of increasing the contact area with the molten steel and adsorbing fine inclusions sufficiently, but conversely, the molten steel passing hole of the partition wall of the molten steel receiving chamber 10 mm to 30 mm for reasons such that clogging is likely to occur and it is difficult to secure a molten steel flow rate to obtain a predetermined casting speed.
Is preferred. If it is too large, the contact area with molten steel becomes small, and the adsorption efficiency of fine inclusions decreases. The diameter and number of the molten steel passage holes are determined in consideration of these points within a range in which the set casting speed can be secured.

Further, as the annular concave (convex) portion formed on the hole wall of the molten steel passage hole, a molten steel vortex effective for increasing the frequency of contact of inclusions with the hole wall is generated, and the intermediate portion adsorbed in the concave portion is generated. It is necessary to prevent the material from flowing out by the molten steel flow for a long period of time, and for that purpose, a plurality of annular recesses having the shape of the annular concave (convex) portion for blocking a part of the molten steel flow. (Labyrinth) is preferable. The depth h and the width x of the concave (convex) portion are normally 0.25 to 1 ... with respect to the hole diameter d of the molten steel passage hole.
If 0, it works effectively. Further, it is preferable that the annular concave (convex) portions are arranged in the length direction (thickness of the partition wall) of the molten steel passage hole by about 3 to 9 lines.

[0013]

【Example】

(Embodiment 1) The present invention will be described below based on Embodiment 1 shown in FIG. The continuous casting machine in this embodiment is of the fixed mold type. In FIG. 1 (a), 1 is a ladle,
Molten steel 2 refined in a converter (not shown) is housed and carried into a tundish 3 of a continuous casting machine. The ladle 1 is provided with a nozzle 5 whose opening is adjusted by a stopper 4.

As shown in FIG. 1 (b), the tundish 3 is provided therein with a partition wall 8 having a large number of molten steel passage holes 7 having a plurality of annular recesses 6 formed in the hole wall. To form a molten steel receiving chamber 9 from the ladle and a molten steel pouring chamber 10 provided with a tundish nozzle 3a for pouring the molten steel into the mold on the bottom wall, and the molten steel 2 from the nozzle 5 of the ladle 1 is formed.
Is introduced into the molten steel injection chamber 10 via the molten steel receiving chamber 9.

Reference numeral 11 is a water-cooled copper mold into which the tip of the tundish nozzle 3a is inserted so as to be immersed in the molten steel in the mold. Reference numeral 12 denotes a mold vibrating device, and 13 denotes a large number of support rolls arranged at the bottom of the mold, which vertically-bends-horizontally supports a cast piece 14 from the mold.

In the continuous casting machine configured as described above, the molten steel 2 in the ladle 1 is injected from the nozzle 5 into the molten steel receiving chamber 9 of the tundish 3 to form a plurality of annular recesses 6 in the hole wall. Through a large number of molten steel passage holes 7
Flows into.

When molten steel passes through the molten steel passage hole 7,
As shown in FIG. 2, a swirl 2v is generated in the molten steel 2 flow by the action of the annular recess 6, fine inclusions in the molten steel flow into the annular recess 6, and after sufficiently flowing there, the corner 6a is adsorbed and separated from the molten steel 2.

As a result, the molten steel 2 is cleaned and flows into the molten steel injection chamber 10 and is continuously supplied from the tundish nozzle 3a through the sliding nozzle SN into the mold. Lubricating powder 15 is also supplied to the molten steel surface of the mold. The molten steel 2 supplied to the mold is cooled by this mold,
A solidified shell 14s is generated, vertically-curved-horizontally supported by a large number of support rolls 13 and continuously drawn out as a slab 14.

As described above, since the molten steel supplied to the mold through the tundish of the present invention has very few inclusions, it is possible to cast a slab of good quality without inclusions.

(Example 2) In the fixed mold type continuous casting machine described above, a tundish having an internal dimension of 1 m x 1 m x 7 m was used, and the diameter d of molten steel flow holes in the partition wall and the number hn of holes were hn: 1.
The casting speed is 1.5 m / min by changing 00 pieces, the thickness t of the partition wall, the depth h of the annular recess, and the number cn of rows (rows) of the annular recess.
With a thickness of 250 mm and a width of 1500 mm, a carbon steel slab slab 14 having the composition shown in Table 1 was cast, a sample was cut from the obtained steel slab slab, and a slime extraction test was performed to determine the amount of inclusions. investigated. The results are shown in Table 2.

[0021]

[Table 1]

[0022]

[Table 2]

As shown in Table 2, in the tundish of the present invention, in order to stably reduce the inclusion index without causing operational problems (insufficient flow rate, clogging, etc.), the partition wall It is necessary to set the conditions such as the hole diameter d of the molten steel passage hole, the number of holes hn, the thickness t of the partition wall, the depth h of the annular recess, the number cn of rows (rows) of the annular recess in a proper range.

From this embodiment, the diameter d of the molten steel passage hole is 15
mm or more, the depth h of the annular recess is 0.25 or more with respect to the diameter d of the molten steel passage hole, the number of threads of the annular recess is 2 to 8, and the thickness t of the partition wall is 100 to 400 mm. , 2,
In the case of 3, 7, 9, 10 the inclusion index in the cast can be reduced without causing operational problems, but in the case of No. 4 with a molten steel passage hole diameter d of 10 mm, the partition wall thickness t
In the case of No. 8 of 500 mm, it was confirmed that operational problems occur.

The level of the inclusion index is shown in comparison with the conventional example as shown in FIG. 3, and in particular, the diameter d is 20 mm and the depth h of the annular recess is 0.5 to 1 with respect to the diameter d. As described above, the number of threads of the annular recess is 4 to 8, and the thickness t of the partition wall is 200 to 400.
It was confirmed that in the cases of Nos. 1, 7, and 9 that satisfy the condition of mm, the amount of inclusions can be significantly reduced compared to the conventional example.

Therefore, in the present invention, in consideration of such results and operating conditions, the diameter d of molten steel flow holes in the partition wall, the number of holes hn, the thickness t of the partition wall, and the depth h of the annular recessed portion. The conditions such as the number of rows (rows) cn of the annular recess are set. The inclusion index here is represented by the inclusion index = log ₁₀ (the number of inclusions having a diameter of 40 to 150 μm / kg).

The tundish of the present invention is not limited to the structure and conditions of the above embodiment. Further, the tundish of the present invention is not only applied to a fixed mold type continuous casting machine, but also to a twin drum type continuous casting machine, a twin belt type continuous casting machine, a single belt type continuous casting machine, a moving mold type continuous casting machine. It is also applied to various continuous casting machines such as machines. Therefore, the structural condition of the tundish of the present invention is changed within the range of the means according to the structural condition of the continuous casting machine to which these are applied.

[0028]

In the tundish of the present invention, a partition wall having a plurality of molten steel passage holes divides the inside of the tundish into a molten steel receiving chamber and a molten steel pouring chamber, and the molten steel from the ladle is received in the molten steel receiving chamber. , Through the molten steel passage hole in which an annular concave (convex) portion is formed in the hole wall.

According to the present invention, due to the action of the annular concave (convex) portion formed in the hole wall of the molten steel passage hole, a swirl is generated in the molten steel flow passing therethrough, and the contact frequency between the hole wall and the fine inclusions is increased. Can be increased. As a result, adsorption of inclusions on the hole walls is promoted, and the molten steel can be cleaned and guided to the molten steel pouring chamber, so that the quality of the obtained slab can be improved after pouring into the mold and cooling. .

[Brief description of drawings]

FIG. 1 (a) is a side cross-sectional schematic explanatory view showing an example of a continuous casting machine using the tundish for continuous casting of the present invention, (b).
The figure is an enlarged front cross-sectional schematic explanatory view of the tundish of FIG.

FIG. 2 is a schematic front view enlarged schematic sectional view of the molten steel passage hole of FIG. 1 (b).

FIG. 3 is a comparative explanatory diagram of inclusion indices in a slab obtained in an example of the present invention and a slab obtained by using a conventional tundish.

FIG. 4 is a side cross-sectional schematic explanatory view showing a structural example of a conventional steel continuous casting machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ladle 2 Molten steel 2v Eddy current 3 Tundish 3a Tundish nozzle 4 Stopper 5 Nozzle 6 Annular recess 7 Molten steel flow hole 8 Partition wall 9 Molten steel receiving chamber 10 Molten steel pouring chamber 11 Water-cooled copper mold 12 Mold vibrating device 13 Support roll 14 Cast piece 14s Solidifying shell 15 Lubricating powder

Claims (1)

[Claims] 1. A molten steel injection chamber in which a partition wall having a plurality of holes through which molten steel can pass is disposed, and a molten steel receiving chamber from a ladle and a nozzle for injecting molten steel into a mold are provided on the bottom wall. In the tundish in which the steel is formed, continuous casting of steel is characterized in that a plurality of annular concave (convex) portions are formed on the inner wall of the molten steel passage hole to generate a vortex in the molten steel to adsorb inclusions. For tundish.