JPH0890177A - Immersion nozzle for continuous casting - Google Patents

Abstract

PURPOSE: To more surely introduce an inert gas for removing inclusions into a casting mold under continuous casting and to more effectively decrease the inclusions of the resulted slab by embedding a perforated body into the inside wall surface near the upper part in the molten metal discharge port of the casting mold, thereby forming gas ejection holes. CONSTITUTION: The discharge port of an immersion nozzle 1 and the perforated body 11 are immersed in a position lower than the surface of the molten steel 6 in the casting mold 5 and an inert gas supplying pipe is connected to a gas introducing port 8, through which pipe, gaseous argon is supplied under pressure at the time of casting. Then, the gaseous argon supplied under pressure to the gas introducing port 8 passes a slit-like gas introducing hole 12 and is blown in a fine bubble form into the molten steel 6 prior to discharge in the immersion nozzle 1 by passing the perforated body 11 having the many fine open pores. The gaseous argon is discharged into the casting mold 5 right thereafter and, therefore, the state of blowing the fine inert gas into the molten steel 6 in the casting mold 5 is attained and the inclusions in the resulted slab are decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dipping nozzle used for pouring molten metal into a mold from a molten metal container such as a ladle or a tundish in continuous casting.

[0002]

2. Description of the Related Art Conventionally, continuous casting of molten steel is carried out by injecting molten steel into a tundish from a ladle and further injecting the molten steel into a mold through a dipping nozzle attached to the outer bottom of the tundish. ing. During this continuous casting,
In continuous casting so far, alumina produced by aluminum added as a deoxidizing agent to molten steel may adhere to the pouring port of the tundish and the inner wall surface of the nozzle thereafter, causing nozzle clogging.

Therefore, in order to prevent the above nozzle clogging, an inert gas such as argon gas or a nitrogen gas (hereinafter referred to as an inert gas) is introduced from an insert nozzle attached to the injection hole of the tundish or a slide valve attached to the outer bottom. However, for the same purpose as this, conventionally, a gas ejection hole is formed in the upper inner wall surface of the immersion nozzle, and the inert gas is blown from the gas ejection hole. . The fine bubbles blown into the nozzle prevent inclusions from adhering to the inner wall surface of the nozzle.

[0004]

By the way, the inert gas blown from the gas ejection holes of the immersion nozzle is for effectively preventing nozzle clogging, and a part of the blown inert gas is , Floats against the molten steel flow in the nozzle injected into the mold from the molten steel container, and traps inclusions in the floating process to prevent nozzle clogging. On the other hand, the remaining inert gas flows into the mold together with the molten steel, but in the process until it flows in, the bubbles coalesce and the bubble diameter increases, so the buoyancy increases and the residence time in the mold shortens. Since the number of particles also decreases, the probability that bubbles will trap inclusions in the mold is small.

As described above, the inert gas blown from the gas ejection holes of the immersion nozzle can prevent inclusions from adhering to the inner wall surface of the nozzle and prevent nozzle clogging, but there is almost no effect of reducing inclusions. As a result of examining the cast slab, it was found that many small inclusions (20 μm or less) remained.

The present invention is based on the above circumstances, and its purpose is to introduce an inert gas for more surely removing inclusions into a mold during continuous casting to obtain a product. The present invention provides a submerged nozzle that can more effectively reduce inclusions of cast slab.

[0007]

In order to achieve the above object, a continuous casting immersion nozzle according to the present invention has a gas ejection hole formed on an inner wall surface near an upper portion of a molten metal discharge port into a mold. Is.

In the continuous casting immersion nozzle, the gas ejection holes may be formed by a porous body embedded in the inner wall surface.

[0009]

It is well known that inclusions can be reduced by blowing an inert gas such as argon gas or nitrogen gas into molten steel. However, in the continuous casting mold,
Since the space between the outer bottom of the tundish and the mold is extremely narrow, it is difficult to directly supply the inert gas into the mold.
Therefore, we tried to flow into the mold by adjusting the amount of gas with a conventional immersion nozzle with gas ejection holes formed in the upper inner wall surface, but as mentioned above, the effect of reducing inclusions in the slab was almost confirmed. There wasn't.

Therefore, the present invention has been completed through the above-mentioned studies, and in the continuous casting immersion nozzle of the present invention, gas ejection holes are formed on the inner wall surface near the upper portion of the molten metal discharge port into the mold. Therefore, when immersed in the mold in continuous casting, the gas ejection holes will be located at a position lower than the molten steel meniscus in the mold, and in the immersion nozzle, an inert gas of fine bubbles blown Can reliably reduce the amount of inclusions in the cast slab by trapping inclusions in the mold by flowing into the mold with molten steel as the majority of fine bubbles without rising in the nozzle. .

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view of a state of use of the continuous casting immersion nozzle according to the present invention, and FIG. 2 is a detailed vertical sectional view thereof.

In the figure, the submerged nozzle 1 is mounted together with a slide valve 3 and a rectifying nozzle 4 mounted on the outer bottom of a tundish 2 as in the conventional submerged nozzle.
It is immersed in the molten steel 6 in the mold 5 during casting, and its shape is, as shown in detail in FIG. 2, a nozzle body 7 made of a refractory material, and a gas introduction formed on the upper outer wall surface of the nozzle body 7. A groove 10 is formed on the inner wall surface near the upper portion of the mouth 8 and the outlet 9 of the nozzle body 7.
And a slit-shaped gas introduction hole 12 formed in the wall between the gas introduction port 8 and the groove 10. In FIG. 1, reference numeral 13 indicates an insert nozzle.

At the time of casting, the discharge port 9 and the porous body 11 of the immersion nozzle 1 are immersed in the mold 5 at a position lower than the molten steel 6 level, and the gas inlet 7 is provided with an inert gas supply pipe. (Not shown) is connected and an inert gas is supplied under pressure. Therefore, during continuous casting, the inert gas pressurized and supplied to the gas introduction port 7 has a slit-shaped gas introduction hole.
After passing through 11 and passing through a porous body 10 having a large number of fine communication holes, fine bubbles are blown into the molten steel 6 before being discharged in the immersion nozzle 1. Immediately after that, since it is discharged into the mold 5, a fine inert gas is blown into the molten steel 6 in the mold 5, and the inclusions in the molten steel 6 are effectively trapped and obtained. Inclusions in the slab can be reduced.

By the way, using the immersion nozzle 1 having the above structure,
Continuous casting of a slab having a 700 mm square cross section was performed while blowing 3 liters of argon gas per minute from only the gas introduction hole 11.
Further, for comparison, continuous casting of a slab with a 700 mm square cross section was performed while blowing the same amount of argon gas from the insert nozzle 13 as in the conventional case to prevent nozzle clogging. Then, the size and the amount of inclusions (index of the amount of inclusions) were investigated at each position shown in FIG. 3 from the center of the obtained cast piece to the outer periphery. The result is shown in FIG.

As is apparent from FIG. 3, in the example of the present invention,
Inclusions with a size of 20 μm or less are significantly reduced at each position compared to the conventional example. It is considered that this is because a large amount of fine inert gas bubbles are present in the mold, and the probability of contact with a large number of small inclusions increases, so that the small inclusions are trapped and easily float.

In the above embodiment, the present invention has been described as an example in which the conventional blowing of the argon gas for preventing the nozzle clogging is stopped, but it goes without saying that they can be used in combination.

[0017]

As described above, with the immersion nozzle for continuous casting according to the present invention, an inert gas for removing inclusions can be surely introduced into the mold during continuous casting, and the obtained casting can be obtained. The inclusions on the piece can be effectively reduced. Moreover, it is possible to more effectively reduce inclusions in the mold while preventing nozzle clogging by using the conventional inert gas for preventing nozzle clogging.

[Brief description of drawings]

FIG. 1 is an explanatory view of a usage state of a continuous casting immersion nozzle according to the present invention.

FIG. 2 is a detailed vertical cross-sectional view of the immersion nozzle for continuous casting according to the present invention.

FIG. 3 is a diagram showing a comparison of the effect of reducing inclusions by blowing an inert gas according to the present invention example and the conventional example.

[Explanation of symbols]

1: Immersion nozzle 2: Tundish
3: Slide valve 4: Straightening nozzle 5: Mold
6: Molten steel 7: Nozzle body 8: Gas inlet
9: Discharge port 10: Groove 11: Porous body 1
2: Gas introduction hole 13: Insert nozzle

Claims (2)

[Claims] 1. An immersion nozzle for continuous casting, characterized in that a gas ejection hole is formed on the inner wall surface near the upper portion of the molten metal discharge port into the mold. 2. The continuous casting immersion nozzle according to claim 1, wherein the gas ejection holes are formed by a porous body embedded in the inner wall surface.