JPH0735642Y2 - Antioxidation device for molten steel in tundish at the start of casting in continuous casting equipment - Google Patents

Description

[Detailed Description of the Invention] <Industrial field of application> The present invention is a continuous casting facility for casting molten steel, which is poured into a tundish from a ladle, into a mold through a sliding nozzle and a dipping nozzle provided in the lower part of the tundish. The invention relates to an apparatus for preventing oxidation of molten steel in a tundish at the start of casting.

<Prior art> When pouring molten steel into a tundish from a ladle, a long ladle nozzle is used as a means to prevent the oxidation of molten steel by air, and the tip of the long nozzle is immersed in the molten steel in the tundish. However, at the start of injecting molten steel from the ladle into the tundish, the molten steel becomes air until the tip of the long nozzle of the ladle is immersed in the molten steel in the tundish. Because of the exposure, the molten steel is significantly oxidized.

If the oxidation products associated with the oxidation of molten steel at the start of molten steel injection from the ladle into the tundish are trapped in the steel, they become non-metallic inclusions and deteriorate the quality of the steel, resulting in defective products. It can be a cause.

Reducing non-metallic inclusions at the start of pouring molten steel from a ladle into a tundish has been an important issue, and various types of antioxidation means have been conventionally proposed.

As an antioxidation means, when starting the injection of molten steel from the ladle into the tundish, there is known a means for introducing and replacing an inert gas such as argon gas into the tundish so as to reduce the oxygen concentration in the tundish. Has been.

That is, when the oxygen concentration in the tundish decreases due to the introduction of an inert gas, the sliding nozzle at the bottom of the tundish is opened immediately before the molten steel is injected from the ladle, and the injection from the ladle is started. There is a method in which pouring from a ladle is started in a state where it is fully closed to collect molten steel in a tundish to secure a required molten steel head, and then a sliding nozzle is opened to start casting into a mold.

In the above, opening the sliding nozzle immediately before pouring molten steel from the ladle means that the tundish is preheated before pouring, but the temperature of the molten steel at the beginning of pouring is low, so keep the sliding nozzle closed. This is because when the injection of the molten steel is started, there is a high possibility that the nozzle will be clogged due to the solidification of the molten steel.

On the other hand, starting the injection of molten steel from the ladle with the sliding nozzle closed and securing the prescribed molten steel head in the tundish and then opening the sliding nozzle is to stabilize the molten steel temperature and keep it in the tundish. This is to prevent contamination of cast molten steel due to existing impurities.

Further, as disclosed in Japanese Patent Laid-Open No. 59-1055, a refractory board made of a tundish bath surface coating is used as a non-oxidizing injection start method for molten steel, and the tundish is divided into two chambers, an upper chamber and a lower chamber. It has been proposed to supply an inert gas to the chamber to prevent the oxidation of molten steel.

<Problems to be solved by the invention> Among the above-mentioned conventional techniques, the one in which the sliding nozzle is opened immediately before the molten steel is injected into the tundish from the ladle is a rising air flow from the nozzle into the preheated tundish. Since the air is entrained by the air, there is a problem that the oxygen concentration in the tundish cannot be reduced sufficiently even though a large amount of inert gas is used.

That is, as shown in FIG. 5, purging argon gas was introduced into the tundish with the sliding nozzle closed (Ar flow rate per unit volume of the tundish was 1.0 min ^−1.
And 1.5 min ^-1 ), the oxygen concentration in the tundish decreases, and the gas is replaced with argon gas in about 3 minutes. However, if the sliding nozzle is opened immediately before the start of pouring from the ladle, air will enter and the acidity concentration will rise to about 5% again, so that the oxidation prevention of the molten steel poured from the ladle will be insufficient.

On the other hand, the method of injecting molten steel from the ladle to the tundish with the sliding nozzle fully closed has the advantage of ensuring the molten steel head in the tundish, but the nozzle clogging is extremely high and there is a problem in operability. In addition to the above, there is a problem that the molten steel is contaminated during the opening work by oxygen when the nozzle is clogged.

In addition, a refractory board made of a bath surface coating that divides the tundish into upper and lower chambers and supplies inert gas to the lower chamber has a problem that the preheating effect rate in the tundish decreases due to the presence of the refractory board. There is a problem of cost increase by using the board. Inadequate preheating and injection of molten steel from the ladle close the sliding nozzle until the molten steel reaches the level of the refractory board, and the molten steel is stored in the tundish, causing solidification of the molten steel in the sliding nozzle and causing operational problems. There is a problem.

The present invention solves the above-mentioned problems of the prior art, prevents the invasion of air into the inert gas that is introduced into the tundish to be replaced, and starts the molten steel injection from the ladle into the tundish. At the start of casting in a continuous casting facility, which can prevent inclusions in the molten steel that are cast into the mold from the tundish through the sliding nozzle and immersion nozzle by preventing oxidation of the molten steel at the same time, and can also prevent nozzle clogging. It is an object of the present invention to provide a device for preventing the oxidation of molten steel in a tundish.

<Means for Solving the Problems> The present invention for achieving the above object is to continuously cast molten steel to be poured into a tundish from a ladle into a mold through a sliding nozzle and a dipping nozzle provided in the lower part of the tundish. A device for preventing the oxidation of molten steel in a tundish at the start of casting in a casting facility, by introducing a steel foil and an inert gas interposed at the joint between the lower end of the sliding nozzle device and the upper end of the immersion nozzle. It is characterized by comprising an inert gas blowing pipe provided in a tundish lid for replacing the atmosphere in the tundish with an inert gas.

The configuration of the present invention will be described below with reference to the drawings. FIG. 1 is a partial sectional view of a continuous casting facility according to the present invention.

In FIG. 1, 1 is a tundish, 4 is a tundish lid, for inserting a long ladle nozzle 8 attached to the lid 4 through a sliding nozzle device 21 provided at the bottom of the ladle 10. The insertion hole 2 and the preheating burner hole 5 are open. 3 is a tundish nozzle hole,
Reference numeral 22 is a cylinder for the sliding nozzle device 21.
Prior to the start of molten steel injection, the tundish 1 is preheated by a preheating burner (not shown), and then the inert gas blowing pipe 6 is brought into the tundish 1 through the inert gas blowing hole 7 of the tundish lid 4. An active gas is blown into the tundish 1 to create an inert gas atmosphere.

Reference numeral 23 denotes a sliding nozzle device whose opening is controlled by a cylinder 24, and a steel foil 15 is provided at a joint between the intermediate nozzle 23a of the sliding nozzle device 23 and the immersion nozzle 12.
The inside of the tundish 1 is sealed by interposing. 14 is a mold.

The sealing means between the intermediate nozzle 23a and the dipping nozzle 12 will be described with reference to FIG.
When the intermediate nozzle 23a of the sliding nozzle device 23 arranged in the lower part of the above is mounted, the steel foil 15 is interposed together with the seal packing 14, and the intermediate nozzle 23a and the immersion nozzle 12 are mounted and sealed. .

Steel foil 1 interposed between the intermediate nozzle 23a and the dipping nozzle 12
The thickness of 5 is preferably 100 μm or less in view of the sealing property of molten steel. Further, in order to completely prevent air from entering from the lower part of the tundish 1 after pouring molten steel from the ladle 10 and to prevent nozzle clogging by the metal, for example, a steel plate is placed on the floor surface of the tundish 1 surrounding the upper part of the tundish nozzle hole 3. Made of start pipe 16
It is desirable that the molten steel is temporarily stored in the tundish 1 and then a large amount of molten steel be supplied at a time so that the steel foil 15 can be melted and passed at once.

<Operation> After the preheating stage is completed, the tundish 1 is moved to the injection position of the continuous casting strand, and then the openings of the tundish lid 4 such as the preheating burner holes 5 are sealed by a sealing means (not shown) such as a sealing lid. Keep it.

The tip of the inert gas blowing pipe 6 is exposed to the space inside the tundish 1 through the inert gas blowing hole 7 of the tundish lid 4, and an inert gas such as argon gas is introduced. At this time, since the joint portion between the lower part of the sliding nozzle device 23 arranged at the lower part of the tundish 1 and the upper part of the immersion nozzle 12 is sealed with the steel foil 15, the sliding nozzle device 23 is kept in the open state. It is possible, but it may be closed at this stage.

Thus, when the inside of the tundish 1 is replaced with the inert gas, the sliding nozzle device 23 is opened if it is closed, and the sliding nozzle device 21 of the ladle 10 is operated to operate the cylinder 22 while introducing the inert gas. When it is switched to open, injection of molten steel is started from the long ladle nozzle 8 into the tundish 1, collides with the tundish bottom convex portion 11, and then flows into the tundish 1.

The molten steel that has flowed into the tundish 1 is blocked by the steel start pipe 16 at 1 o'clock and stored, but the heat of the molten steel causes the start pipe 16 to melt and pass through the sliding nozzle device 23 in the open state all at once. Since a large amount of molten steel is supplied, the steel foil 15 is instantly melted and passed, and casting into the mold 14 is started via the immersion nozzle 12.

The molten gas injected into the tundish 1 is continuously blown with the inert gas until the molten steel surface rises and reaches the ladle long nozzle 8, and the injection is performed while preventing the molten steel from being oxidized. Then, when the tip of the ladle long nozzle 8 is immersed in the molten steel, flux is added to melt the molten steel and the introduction of the inert gas is stopped in a state of covering the molten steel surface. Thus, the molten steel in the tundish 1 is held at a predetermined level, and casting into the mold 14 is performed.

Fig. 3 shows the transition of oxygen concentration in the tundish when argon gas was supplied into the tundish with the opening of the tundish lid sealed and the upper part of the immersion nozzle sealed with steel foil as described above. Shows.

It can be seen from FIG. 3 that after the tundish was replaced with argon gas, even if the sliding nozzle device was opened prior to the start of the injection, the steel foil was sealed so that the injection could be started without the oxygen concentration rising. I understand. At this time, the oxygen concentration was adjusted to 0.5 by introducing an argon gas amount of at least four times the tundish volume.
% Or less.

As shown in Fig. 4, the oxygen concentration in the tundish was adjusted to 0.5.
% Or less, the inclusion defects in the bottom slab are 1/10 of the conventional method.
It can be reduced to the following.

<Example> An example of the present invention will be described below.

The tundish opening was sealed with asbestos and refractory wool, and refractory wool was laid between the tundish and the tundish lid to eliminate the gap. Further, the gap between the intermediate nozzle and the dipping nozzle of the sliding nozzle device was sealed with a stainless steel foil having a thickness of 40 μm by the means shown in FIG.

In addition, an iron start pipe with a height of 300 mm was installed in the tundish nozzle hole. The internal volume of the tundish is 4
m is ^3. After completion of the tundish preheating, when argon gas was supplied into the tundish at a flow rate of 4 Nm ³ / min,
The sliding nozzle was opened 1 minute before pouring the molten steel from the ladle, but the oxygen concentration in the tundish at the time of pouring the molten steel (4 minutes after Ar started) dropped to 0.35%. as a result,
The occurrence rate of inclusion property defects in the bottom slab was 0.2%, which was reduced to about 1/20 of the conventional method shown below.

In the same tundish as the example, in the comparative example in which the intermediate nozzle and the dipping nozzle were not sealed with the steel foil, the same operation performed, the oxygen concentration in the tundish at the time of injection was 4.5%, and the bottom slab The incidence rate of inclusion-related defects was 3.6%.

<Effect of the Invention> Since the present invention is configured as described above, it is possible to prevent the secondary oxidation of molten steel in the tundish at the start of casting, and to prevent the inclusion physical defect of the bottom slab at the beginning of casting. In addition to achieving stable quality and improved yield of continuous slabs, nozzle clogging at the beginning of casting is eliminated.

[Brief description of drawings]

FIG. 1 is a partial vertical cross-sectional view of a continuous casting facility according to the present invention, FIG. 2 is a partial vertical cross-sectional view showing an essential part of the present invention, and FIG. 3 is a time-dependent change in oxygen concentration in a tundish according to the present invention. FIG. 4 is a graph showing the relationship between the oxygen concentration in the tundish before injection of molten steel and the occurrence rate of physical defects in the bottom slab.
FIG. 5 is a graph showing changes over time in the oxygen concentration in the tundish by the conventional apparatus. 1 ... Tundish, 4 ... Tundish lid, 6 ...
… Inert gas blowing pipe, 8 …… Ladle long nozzle, 10 ……
Ladle, 12 ... Immersion nozzle, 14 ... Seal packing, 15 ...
… Steel foil, 16 …… Start pipe, 21 …… Sliding nozzle device, 23 …… Sliding nozzle device,
23a ... Intermediate nozzle.

Claims (1)

[Scope of utility model registration request] 1. An apparatus for preventing the oxidation of molten steel in a tundish at the start of casting in a continuous casting facility in which molten steel injected from a ladle into a tundish is cast into a mold through a sliding nozzle and a dipping nozzle provided in the lower part of the tundish. It is a tank for replacing the atmosphere in the tundish with an inert gas by introducing a steel foil and an inert gas interposed at the joint between the lower end of the sliding nozzle device and the upper end of the immersion nozzle. An apparatus for preventing the oxidation of molten steel in a tundish at the start of casting in a continuous casting facility, which comprises an inert gas blowing pipe provided on a dish lid.