JPH06170505A - Immersion nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To surely prevent the clogging of an immersion nozzle by adding K2O on the inner wall surface at the lower part of an inner hole body for gas blowing from the inner hole body and easily progressing the clogging and using a material reduced in SiO2 content, in combination. CONSTITUTION:In the immersion nozzle for continuously casting a steel, SiO2 content in the inner hole body 1 corresponding to a gas blowing part is made to be <=5wt.%. Further, at least the inner wall surface at the lower part containing discharging holes 2 from the inner hole body 1 is constituted with the refractory of 1-10wt.% K2O content and <=5wt.% SiO2 content. By using the material A adding this K2O to the inner wall of the nozzle, K2O in the refractory and Al2O3 in the molten steel are reacted to produce a low melting point material. By this method, the clogging of the nozzle can surely be prevented and further, trouble of blow hole kind defect is not developed and the quality of a steel plate is stabilized and also, the yield is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection type immersion nozzle used for casting molten steel from a tundish into a mold in continuous casting of steel.

[0002]

2. Description of the Related Art At present, in continuous casting, an immersion nozzle is used to supply molten steel from a tundish into a mold without oxidizing it. As the material of the dipping nozzle, Al ₂ O ₃ and C are mainly used, and 20
Those containing about ₂ wt% of SiO ₂ are mainly used. In such a submerged nozzle, alumina and metal ingots deposited in steel adhere to the inner wall of the nozzle as the casting time elapses, and when violent, the nozzle may be clogged and the casting may be stopped.

As one of means for solving this problem, for example, as shown in Japanese Patent Publication No. 58-3467,
It is known to insert a porous cylindrical refractory (inner hole body) that is concentric with the inner hole of the immersion nozzle into the main body of the immersion nozzle and blow Ar or another inert gas from the inner wall of the porous refractory. This gas blowing reduces the contact area between the inner surface of the nose and the molten steel and further stirs the molten steel, or forcibly separates the deposits by gas bubbles to cause the growth of alumina inclusions on the inner wall surface of the nozzle. It has the effect of preventing.

[0004]

However, various methods have been adopted as a method of blowing gas from the inner wall of the immersion nozzle. However, these are mainly those in which the inner hole body corresponding to the gas blowing portion is provided above the discharge hole. Therefore, there has been a problem that alumina adheres and deposits in the vicinity of the discharge holes to which Ar gas does not reach. Further, the Ar bubbles blown in are partly captured by the solidification interface while floating in the mold,
It becomes a cause of bubble-type defects that occur after hot rolling and cold rolling. In view of these problems, the present invention is intended to provide a continuous casting immersion nozzle capable of casting a stable steel plate material without bubble defects, while preventing nozzle clogging. is there.

[0005]

DISCLOSURE OF THE INVENTION According to the present invention, in the immersion nodule for continuous casting of steel, the SiO ₂ content of the inner hole body corresponding to the gas blowing portion is set to 5 wt% or less, The present invention relates to a continuous casting immersion nozzle, wherein the lower inner wall surface is made of a refractory material having a K ₂ O content of 1 to 10 wt% and a SiO ₂ content of 5 wt% or less.

[0006]

In order to prevent clogging of the immersion nozzle, an inert gas such as Ar gas is blown from the portion where the alumina adhesion progresses to form a gas film between the molten steel and the inner wall of the nozzle, or the adhered matter is gas bubbled. The most reliable method is to force the peeling. However, as shown in FIG. 1, when Ar gas is blown from the inner hole body 1 of the immersion nozzle,
Although the adhesion of alumina to the inner hole body 1 and its periphery can be reliably prevented, there is no direct gas injection from the inner wall as in the vicinity of the discharge hole 2, and the flow changes drastically, increasing the frequency of collision of alumina in molten steel with the wall surface. In the region, the effect of preventing nozzle clogging by Ar gas cannot be sufficiently obtained.

Therefore, the inventors of the present invention added K ₂ O to the inner wall surface of the lower portion 3 of the inner hole body, in which the gas is blown from the inner hole body 1 and the clogging is likely to progress, and the SiO ₂ content is reduced. A
By using this together, it was possible to reliably prevent the clogging of the immersion nozzle.

By using the material A to which K ₂ O is added for the inner wall of the nozzle, K ₂ O in the refractory and Al ₂ O _{3 in the} molten steel are reacted with each other to form a low melt. This low melt is washed away by the molten steel flow and the air bubbles blown from the inner hole body 1 to give a minute melting loss to prevent the adhesion.

Further, SiO ₂ in the refractory material is Al in the molten steel.
Since it reacts with Al ₂ O ₃ to generate Al ₂ O ₃ , it is necessary to reduce SiO ₂ in the refractory as much as possible from the viewpoint of preventing the adhesion of alumina. According to the present invention, a synergistic effect of lowering the melting point of the deposit by K ₂ O addition and exfoliating the deposit of Ar bubbles can be obtained, and the anti-adhesion effect can be maintained even when the casting time is long and the molten steel cleanliness is deteriorated. You can

On the other hand, when the gas is blown from the submerged nozzle inner hole body 1, a bubble type defect becomes a problem. However, when Ar gas blowing is carried out, bubble-type defects do not occur in all the slabs, but tend to occur frequently in the latter half of casting.

Further, it is known that Ar bubbles trapped in a slab are not crimped after hot rolling or cold rolling as they are larger, and appear as swelling defects on the surface of a steel sheet. Based on such knowledge, the present inventors considered that the coarsening of Ar bubbles in the latter half of casting was one of the causes of the bubble system defect, and have conducted detailed investigations on the factors that cause coarsening of bubbles.

As a result, the SiO 2 in the immersion nozzle inner hole body 1
It was found that since ₂ is reduced by C and disappears, the porosity and the pore diameter of the inner pore body 1 are increased in the latter half of the casting, and the Ar bubble diameter generated thereby is coarsened. Therefore, by reducing the amount of SiO ₂ in the inner pore body 1, it is possible to suppress the coarsening of the bubbles and thereby prevent the bubble-based defects.

Further, since the fine Ar gas can be uniformly blown from the entire surface of the inner hole body 1 by reducing the SiO ₂ , the nozzle clogging can be effectively prevented, and the Ar gas flow rate can be improved from the viewpoint of bubble system defects. It is also possible to lower.

As shown above, the SiO in the inner pore body 1
_{2 The} content rate is reduced, and K ₂ O is contained on the inner wall surface of the lower portion 3 below the inner hole body including at least the discharge hole 2, and further SiO _{2 is} added.
By applying the material A in which the water content is reduced, it is possible to reliably prevent the immersion nozzle from being clogged and to provide an immersion nozzle for continuous casting in which no bubble-type defects occur.

In the present invention, it is preferable that the inner pore body 1 does not contain SiO ₂ , but if necessary 5 wt%
You may add only in the following. This is because if the SiO ₂ content is 5 wt% or less, even if all of the SiO ₂ in the inner pore body 1 disappears, there is almost no change in the porosity and the pore diameter, and bubble-type defects do not occur.

The material A applied to the lower portion 3 of the inner hole body including the discharge hole 2 has a K ₂ O content of 1 to 10 wt%, SiO ₂
It is an alumina graphite material with a content of 5 wt% or less. When the content of K ₂ O is less than 1 wt%, a liquid phase is not generated even when it reacts with Al ₂ O _3, and the effect of preventing adhesion cannot be obtained. If the K ₂ O content exceeds 10 wt%, Al ₂
The liquid phase ratio generated by the reaction with O ₃ becomes 20% or more, and the corrosion resistance of the immersion nozzle itself is lowered.

SiO ₂ reacts with Al in molten steel to form Al ₂ O ₃
Therefore, it is desirable not to contain it in the nozzle, but if necessary from the viewpoint of spalling resistance, it is 5 wt.
% Or less may be used. This is because when the SiO ₂ content exceeds 5 wt%, the amount of Al ₂ O ₃ produced increases and the anti-adhesion effect cannot be obtained sufficiently.

Although the basic constituent components of the immersion nozzle are as described above, other materials which are already known as additives to the nozzle material may be contained within the range not impairing the effects of the present invention. . For example, in order to improve strength, metal S
i in order to prevent oxidation and improve spalling resistance
It is also possible to combine etc. Further, it is desirable to use the above-mentioned material also for the nozzle body excluding the inner hole body lower part 3 including the inner hole body 1 and the discharge hole 2.

[0019]

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples. To the raw material-containing material shown in Table 1, 15 wt% of a phenol resin was added as a resin binder to the outside and kneaded, and an isostatic press was used.
It was molded into a nozzle shape shown in FIG. 1 at a pressure of 0 t / cm ² . Refractory C in the powder line is made of ZrO ₂
The ZrO ₂ -C material containing 5 wt% and 25 wt% C was unified.

[0020]

[Table 1]

Further, this molded body is subjected to reduction firing at a temperature of 1200 ° C., and a gas blowing type immersion nozzle for continuous casting (outer diameter 185 mmφ, inner diameter 90 mmφ, discharge hole diameter 70 mm).
An inverted Y-shaped nozzle having φ, a discharge hole angle of 35 degrees, and an inner hole thickness of 15 mm was produced. Using the immersion nozzle thus obtained, a carbon concentration of 30 containing Ti of 0.08 wt% was obtained.
Ultra low carbon steel of ppm was cast for 400 minutes. At this time, A
The flow rate of gas sprayed with t was 6 Nl per ton of molten steel. In both the example and the comparative example of the present invention, the casting size is 24
5 mm × width 1500 mm, cut into length 8500 mm to make one coil unit. This slab is hot-rolled and cold-rolled by a conventional method, and finally has a thickness of 0.7 mm and a width of 1500.
It was a cold rolled steel plate of mm coil. The evaluation of the immersion nozzle for bubble defects was performed by visual observation on an inspection line after cold rolling and by the number of bubble defects generated per coil. Regarding the evaluation of the clogging of the immersion nozzle, after collecting the immersion nozzle after casting, the maximum adhesion thickness immediately above the discharge hole was measured, and this was divided by the casting time to calculate the adhesion speed. Table 2 shows the quality evaluation results of the examples and comparative examples.

[0022]

[Table 2]

As shown in Table 2, in the embodiment, S of the inner hole body 1 is
The content of iO ₂ is 5 wt% or less, and the inner wall surface of the lower portion 3 including at least the discharge hole is made of a material having a K ₂ O content of 1 to 10 wt% and a SiO ₂ content of 5 wt% or less. By doing so, it was possible to always stably prevent the nozzle clogging. Further, not only in terms of operation but also in terms of quality, there were no bubble-type defects, and a very good cast piece could be obtained.

On the other hand, in Comparative Example 1, K
_{Since the 2} O ₂ content was less than 1 wt%, the effect of preventing nozzle clogging was not sufficiently obtained, and the production was stopped 300 minutes after the start of casting. Further, in Comparative Example 2, since the K ₂ O content in the lower portion 3 of the inner hole exceeded 10 wt%, the corrosion resistance of the immersion nozzle decreased and the melting loss proceeded. Moreover, Comparative Example 3 SiO since SiO ₂ content of the immersion nozzle hole member 1 exceeds 5 wt% ₂
Due to the disappearance, the porosity and the pore diameter increased, and bubble-type defects frequently occurred in the latter half of casting. The above results are the results of testing the structural nozzle shown in FIG. 1, but similar effects were obtained with the structural nozzles shown in FIGS.

[0025]

As described above, according to the immersion nozzle for continuous casting of the present invention, the nozzle clogging can be surely prevented, and the problem of bubble system defect does not occur, so that the quality of the steel sheet is very stable. However, the yield is also significantly improved. Also,
Since various unsteady operations due to nozzle clogging are eliminated, it is possible to provide an immersion nozzle that is effective in terms of operation.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the structure and material of a nozzle.

FIG. 2 is a diagram for explaining the structure and material of a nozzle.

FIG. 3 is a diagram for explaining the structure and material of a nozzle.

[Explanation of symbols]

1 Uchianatai second ejection hole 3 in the hole body lower _{A K 2 O-Al 2 O} 3 -C material B Al ₂ O ₃ -C material C ZrO ₂ -C material

Claims (1)

[Claims] 1. An immersion nozzle for continuous casting of steel, wherein an SiO ₂ content of an inner hole body corresponding to a gas blowing portion is 5 wt.
%, And the inner wall surface below the inner hole body including at least the discharge hole has a K ₂ O content of 1 to 10 wt%, SiO ₂
An immersion nozzle for continuous casting, comprising a refractory material having a content of 5 wt% or less.