JP2002205149A - Immersion nozzle for continuously casting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an immersion nozzle with which clogging of the nozzle caused by Al2O3 can be prevented without damaging cleanliness of a cast slab and also, obstructing stability of a continuous casting operation. SOLUTION: The clogging problem is dissolved by using the immersion nozzle 6 for continuous casting, in which a slit 7 is arranged in this side wall, and filling material 8 composed of CaO powder and carbon powder is filled in this slit. Further, in this immersion nozzle, this problem is dissolved at easier by adding what the slit is shut off from the atmosphere, inert gas is supplied into the slit, the pressure in the slit is higher than the atmosphere and the grain diameter of the CaO powder is regulated to <=3 mm and the grain diameter of the carbon powder is regulated to <=0.5 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an immersion nozzle for supplying molten steel into a mold in continuous casting of steel, and more particularly to an immersion nozzle capable of preventing clogging of the immersion nozzle with Al ₂ O _3. It is.

[0002]

2. Description of the Related Art Oxidized and refined molten steel is usually deoxidized by Al, and oxygen in the molten steel which has been increased by the oxidizing and refining is removed. However, the generated Al ₂ O ₃ particles are mixed with molten steel and Al ₂ O _3.
There is a limit to the floating separation from the molten steel due to the density difference from O _3, and therefore, fine Al ₂ O ₃ particles remain in the molten steel in a suspended state. In addition, in order to stably reduce the oxygen in the molten steel, Al is dissolved in the molten steel after Al deoxidization, and this Al comes into contact with the atmosphere during the injection process from the ladle to the tundish or in the tundish. When oxidized, Al ₂ O ₃ is generated. The Al ₂ O ₃ suspended in the molten steel adheres to the inner wall of the immersion nozzle when passing through the immersion nozzle made of Al ₂ O ₃ -graphite.
Accumulation and blockage of the immersion nozzle occurs.

When the immersion nozzle is closed, various problems occur in the casting operation and in the quality of the slab. For example, the slab drawing speed has to be reduced, which not only reduces the productivity, but also, in severe cases, necessitates stopping the casting operation itself. Also, Al ₂ deposited on the inner wall of the immersion nozzle
O ₃ is suddenly exfoliated and discharged as large Al ₂ O ₃ particles into the mold. If this is trapped in the solidified shell in the mold, it becomes a product defect. Molten steel flows out when pulled directly below, causing
It can even lead to kuout. For these reasons, the mechanism of adhesion and deposition of Al ₂ O _{3 on} the inner wall of the immersion nozzle and its prevention method have been studied in the past.

[0004] Conventional Al ₂ O ₃ deposition mechanisms include: Al ₂ O ₃ suspended in the molten steel collides with the inner wall of the immersion nozzle and deposits; and the temperature of the molten steel passing through the immersion nozzle decreases, and The solubility of Al and oxygen in the molten steel decreases, and Al ₂ O ₃ crystallizes and adheres to the inner wall .: SiO ₂ in the immersion nozzle and graphite react to form SiO,
This reacts with Al in the molten steel to form Al ₂ O ₃ on the inner wall of the immersion nozzle, which covers the inner wall of the immersion nozzle, on which fine Al ₂ O ₃ particles suspended in the molten steel collide and deposit. It is recommended to do so.

[0005] Then, according to these adhesion and deposition mechanisms: Ar gas is blown into the inner wall of the immersion nozzle to form a gas film between the inner wall of the immersion nozzle and the molten steel so that Al ₂ O ₃ does not contact the wall. , Using an immersion nozzle made of a material with a reduced amount of added SiO _{2 as} an oxygen source, and using Al ₂ O ₃
Suppressing the generation of: combines with Al ₂ O ₃ in the immersion nozzle material is contained ingredients to make a low-melting compound, to efflux Al ₂ O ₃ adhered to the immersion nozzle inner wall as a low melting compound,: immersion nozzle inner wall In order to keep the temperature of the molten steel from falling, the outer wall of the immersion nozzle is covered with an insulating sleeve, or two layers are used to reduce the amount of heat transfer from the wall of the immersing nozzle. Measures for preventing Al ₂ O ₃ adhesion, such as installation in the middle, have been proposed.

[0006]

However, the above countermeasures have the following problems. That is, in the above measures, a part of Ar blown into the immersion nozzle cannot be diffused from the surface of the molten steel in the mold and is captured by the solidified shell. Ar
Inclusions are often found at the same time in the pores generated by the trapping of this, which causes product defects. Further, when the pores are trapped in the surface layer of the slab, the inner surface of the pores is oxidized in a continuous casting machine or in a heating furnace before rolling, which may not be scaled off and may result in a product defect.

[0007] In the above measures, S in the material of the immersion nozzle
Since iO ₂ is reduced, the thermal shock resistance of the immersion nozzle is deteriorated. Usually, the immersion nozzle is used after preheating. This is because the refractory cracks easily due to thermal shock. SiO ₂
Has an extremely high effect of improving thermal shock resistance, and by lowering the content of SiO ₂ , the frequency of occurrence of cracks in the immersion nozzle becomes extremely high immediately after the passage of molten steel at the start of casting.

In the above countermeasures, for example, CaO and A are added by adding CaO as a constituent material of the immersion nozzle.
Although it is possible to combine with l ₂ O ₃ to form a low melting point compound and to inject this low melting point compound together with molten steel into a mold to prevent Al ₂ O _{3 from} adhering to the inner wall of the immersion nozzle,
Since the low-melting point compound that causes inclusions flows out into the mold, there is a problem that the cleanliness of the slab is deteriorated. Furthermore, since the inner wall of the immersion nozzle wears out, it is not suitable for long-time casting.

Further, the above measures have an effect of preventing solidification of steel on the inner wall of the immersion nozzle, but have a small effect of preventing adhesion of Al ₂ O ₃ . It can also be understood from the fact that Al ₂ O ₃ adheres and accumulates a lot even in the nozzle inner wall portion immersed in the molten steel.

[0010] As described above, the conventional measures for preventing Al ₂ O _{3 from} adhering include increasing the number of inclusions in the slab or impeding the stability of operation, even if the clogging of the immersion nozzle can be prevented. Al ₂ that is satisfactory in all aspects of operation, slab quality
In fact, measures to prevent O ₃ adhesion have not yet been established.

The present invention has been made in view of the above circumstances,
The purpose is to prevent the immersion nozzle from being clogged by Al ₂ O ₃ in the molten steel during continuous casting of molten steel without impairing the cleanliness of the slab and without impairing the stability of the continuous casting operation. It is to provide an immersion nozzle for continuous casting that can be prevented.

[0012]

Means for Solving the Problems The present inventors have conducted some basic experiments on the mechanism of depositing Al ₂ O ₃ on a submerged nozzle in order to solve the above problems. Hereinafter, the experimental method and the experimental result will be described in detail.

As shown in FIG.
Al-killed steel in high-frequency melting furnace 22 whose atmosphere is adjusted with Ar
Is melted, and the immersion nozzle material and
Al used as_Two O_Three -Made of graphite refractories
A test piece 28 having a diameter of 25 mm was immersed. Al_Two O_Three 
-Graphitic refractories have a porosity in the range of 16-30%.
Changed to 5 levels. The inner diameter of the test piece 28 is
A hole of 10 mm is provided, and in this hole, the particle diameter is 0.5 to
3mm CaO powder and particle diameter 0.01-0.5m
m of carbon powder at a mass ratio of 1: 1. still,
FIG. 1 shows Al_Two O _Three Basic experiments to elucidate the adhesion mechanism
FIG. 1 is a schematic diagram of the method, wherein in FIG.
Is high Al_Two O_Three The quality crucible, 26, is a thermocouple.

Filling 8 composed of CaO powder and carbon powder
Ar was supplied at a rate of 100 ml / min into the hole in which was formed, and the Ar pressure in the hole was set to be 50 kPa higher than the atmospheric pressure. Then, after elapse of 10 minutes after immersing the test piece 28,
The pressure in the chamber 23 was reduced to 67 kPa, held in that state, and immersed in the molten steel 12 for a total of 60 minutes. Thereafter, the test piece 28 was pulled up, and the thickness of the adhesion layer and the deposit attached to the outer surface wall of the test piece 28 Was identified. The components of the molten steel 12 are: C: 0.04 to 0.05 mass%, Si: 0.02
mass% or less, Mn: 0.15 to 0.20 mass%, P:
0.01 to 0.016 mass%, S: 0.008 to 0.0
13 mass%, Al: 0.06 to 0.12 mass%.

For comparison, a solid test piece 28 having no pores was also immersed, and the thickness of the adhered layer adhered to the outer surface wall and the adhered substance were identified. In the case of the solid test piece 28, a solid test piece holder having no hole was used, and the test piece 28 was immersed without supplying Ar. Table 1 shows the chemical components and apparent porosity of the five Al ₂ O ₃ -graphitic refractories used as the test pieces 28.

[0016]

[Table 1]

The test piece 28 was taken out of the molten steel 12 after being immersed in the molten steel 12 for 60 minutes, and the results of measuring the thickness of the adhesion layer determined from the diameter of the test piece 28 are shown in Table 1. As shown in Table 1, the thickness of the attached matter is much smaller in the case of a test piece filled with CaO powder and carbon powder and supplied with Ar than in the case of a solid test piece. Do you get it. This deposit is mainly Al ₂ O ₃ , and
In the test piece filled with the CaO powder and the carbon powder, a reaction product of CaO and Al ₂ O ₃ was observed near the boundary between the main body of the test piece and the deposit.

Further, as shown in Table 1, the relationship between the thickness of the deposit after immersion for 60 minutes and the apparent porosity of the test piece shows that as the apparent porosity increases, the thickness of the deposit decreases. Was. However, when the porosity exceeded 28%, it was observed that the molten steel infiltrated into the pores of the test piece and the test piece became slightly eroded. Therefore, it was found that increasing the porosity to 28% or more was dangerous. In addition, from the result of the examination of the test piece pulled up during the immersion, it was also found that the thickness of the deposit increased in proportion to the immersion time.

Next, tests were conducted in which the mass ratio of the CaO powder to the carbon powder constituting the filler 8 and the particle size of the CaO powder and the particle size of the carbon powder were changed. The mass ratio is Ca
The O content was changed to six levels of 20 to 70 mass%. Particle size change, the particle diameter of CaO powder is less than 0.5 mm,
On the other hand, the carbon powder has a particle diameter of less than 0.01 mm and a particle diameter of less than 0.01 to 0.3 mm.
Three levels, 5 mm and 0.5 mm, were tested in combination. The test method is the same as the method in which the influence of the apparent porosity of the test piece 28 was investigated.

Table 2 shows the test conditions and the measurement results of the thickness of the adhered layer after immersion for 60 minutes. Test No.B shown in Table 2
-1 to 6 are tests in which the mixing ratio of the filler was changed,
Test Nos. B-7 to B-8 have a CaO powder particle diameter of 0.5 m.
m or more than 3 mm, and the test Nos. B-9 to B-10 have particle diameters of carbon powder of 0.01 mm.
The test was changed to less than 0.5 mm or more than 0.5 mm. As shown in Table 2, in the mixing ratio of CaO powder and carbon powder, when the mixing amount of carbon powder is 30 mass% or more, Al
₂ O ₃ deposition amount of decline was observed, it was found that the amount of carbon powder is reduced and most Al ₂ O ₃ deposited thickness in the range of 40~60mass%. In addition, it was found that the finer the CaO powder and carbon powder, the greater the adhesion prevention effect. In these basic experiments, quicklime powder was used as CaO powder, and graphite powder was used as carbon powder.

[0021]

[Table 2]

The present invention has been made based on the above test results, and the immersion nozzle for continuous casting of steel according to the first invention is:
In a continuous casting immersion nozzle for supplying molten steel into a mold, a slit is provided on a side wall thereof, and the slit is filled with CaO powder and carbon powder. The immersion nozzle for casting according to the first invention is characterized in that the slit is shielded from the atmosphere in the first invention, and the immersion nozzle for continuous casting of steel according to the third invention is characterized in that in the first invention, Wherein the inside of the slit is higher than the atmospheric pressure, wherein the immersion nozzle for continuous casting of steel according to the fourth invention is the immersion nozzle according to any one of the first invention to the third invention, The particle diameter of the CaO powder is 3 mm or less, and
The particle diameter of the carbon powder is 0.5 mm or less, and the immersion nozzle for continuous casting of steel according to the fifth invention is the immersion nozzle according to any one of the first invention to the fourth invention, wherein The inner wall of the immersion nozzle of the inner part is 19-
The immersion nozzle for continuous casting of steel according to the sixth invention is characterized in that it is made of a refractory having a porosity of 24%, and the slit according to any one of the first to fifth inventions, At least 100 from the top of the immersion nozzle
It is characterized by being installed up to a range below mm.

In the present invention, a slit is provided on the side wall of the continuous casting immersion nozzle, and the slit is filled with CaO powder and carbon powder. The immersion nozzle is heated to about 800 to 1200 ° C. by molten steel passing through the immersion nozzle,
The CaO powder and the carbon powder filled in the inner wall of the immersion nozzle are also heated. With heated CaO powder and carbon powder,
A reaction of CaO (s) + C (s) → Ca (g) + CO (g) occurs, and Ca gas and CO gas are generated in the slit.

Incidentally, the refractory material constituting the immersion nozzle usually has a porosity of 10 to 20%. When supplying molten steel into the mold via the immersion nozzle, a sliding nozzle or a stopper is used.
While controlling the flow rate while reducing the cross-sectional area in the middle, that is, the cross-sectional area of the sliding nozzle part or the stopper part is smaller than the cross-sectional area of the immersion nozzle, molten steel flows at high speed In the immersion nozzle, the pressure is always reduced and becomes lower than the atmospheric pressure.

Therefore, Ca gas and CO gas generated in the slit pass through the side wall of the immersion nozzle and permeate the inner wall surface of the immersion nozzle. Molten steel exists on the inner wall surface side of the immersion nozzle, and Ca gas and CO gas react with Al in the molten steel, Ca gas returns to CaO, and CO gas becomes Al ₂ O.
₃ is formed and dissolved as C in molten steel.

As described above, on the inner wall surface of the immersion nozzle,
CaO and Al_Two O_Three A mixture of sintering
In response to CaO-Al_Two O_Three To low melting point compound
You. As a result, the low-melting point compound is converted from the inner wall of the immersion nozzle.
Deposits flowed out and Al_Two O _Three The adhesion thickness is suppressed
You.

However, when Ca gas and CO gas generated in the slit are brought into contact with air, these gases are oxidized to CaO and CO ₂ gas, and the above effects are not exhibited. Therefore, it is important to block the slit from the atmosphere or supply an inert gas into the slit to make the inside of the slit higher than the atmospheric pressure to prevent oxidation of these gases. When an inert gas is supplied into the slit, the inert gas also passes through the side wall of the immersion nozzle to form a gas film between the inner wall surface of the immersion nozzle and the molten steel, thereby preventing Al ₂ O ₃ from adhering. The effect can also be exhibited.

[0028]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a view showing an example of an embodiment of the present invention, and is a schematic view of a front vertical cross section of a mold portion of a continuous casting facility, and FIG. 3 is an enlarged view of an immersion nozzle according to the present invention.

As shown in FIG. 2, above the mold 1 composed of the opposed long side copper plate 2 of the mold and the opposed short side copper plate 3 contained in the long side copper plate 2 of the mold, A tundish 4 made of refractory is arranged. An upper nozzle 17 is provided at the bottom of the tundish 4. The upper nozzle 17 is connected to the upper nozzle 17, and a fixed plate 18, a sliding plate 19,
And sliding nozzle 5 made of rectifying the nozzle 20 is disposed, further, the lower surface side of the sliding nozzle 5, Al ₂ O ₃ - graphite and _{Al 2 O 3 -SiO 2 - Al} 2 O 3 and graphite graphite etc. A immersion nozzle 6 made of a refractory whose main component is, is provided, and a molten steel outflow hole 21 from the tundish 4 to the mold 1 is formed.

As shown in FIG. 3, the immersion nozzle 6 is provided with a slit 7 on its side wall, and a CaO
A filling 8 consisting of powder and carbon powder is formed.
Further, a gas introduction pipe 11 for supplying an inert gas such as Ar into the slit 7 is connected to the slit 7. A slag line section 10 made of a refractory material having excellent slag erosion resistance is provided in an outer peripheral portion of the immersion nozzle 6 in a range where the slag line section 10 comes into contact with the mold powder 15.

The slit 7 can be formed as follows. When the immersion nozzle 6 is formed, for example, a string-like substance that disappears at the firing temperature is inserted into a predetermined position on a side wall of the immersion nozzle 6, and the substance is lost when the immersion nozzle 6 is fired, thereby forming the slit 7. can do.
Further, the filling material 8 is provided in the slit 7 formed in this manner.
It can be obtained by charging a mixture of CaO powder and carbon powder from outside the immersion nozzle 6. The filling degree of these powders may be low. The point is that during the period from the start of casting to the end of casting, it is sufficient to charge the slit 7 with the amount of CaO powder and carbon powder that exist. As the CaO powder source, quicklime can be used, and as the carbon powder source, graphite, charcoal, coke, or the like can be used.

As described above, the compounding ratio of the CaO powder and the carbon powder is preferably in the range of 40 to 60 mass% from the viewpoint of suppressing the adhesion of Al ₂ O ₃ . The finer the CaO powder and carbon powder, the more A
Since the effect of suppressing l ₂ O ₃ adhesion is high, the particle diameter of the CaO powder used is 3 mm or less, and the particle diameter of the carbon powder is 0.5
mm or less. The particle diameter as used herein refers to a size that passes through a 3 mm sieve and a 0.5 mm sieve, respectively.

The installation range of the slit 7 is preferably at least the upper end from the upper end of the immersion nozzle 6 to a position 100 mm below. The present inventors have confirmed that the amount of Al ₂ O ₃ attached can be suppressed by covering the filling nozzle 8 with a range of 100 mm below the upper end of the immersion nozzle 6. This is presumably because the Ca gas and CO gas permeated into the immersion nozzle 6 are carried downstream along the flow of molten steel, so that it is not necessary to extend the installation range of the filler 8. However, if the slit 7 is installed up to the upper end of the immersion nozzle 6, the strength of the immersion nozzle 6 is reduced. Therefore, it is preferable not to install the slit 7 in a range at least 20 mm from the upper end of the immersion nozzle 6. Similarly, it is desirable to provide the slit 7 in the entire circumferential direction of the immersion nozzle 6. However, in order to prevent the strength of the immersion nozzle 6 from deteriorating, the area where the slit 7 is not provided is set at several places in the circumferential direction of the immersion nozzle 6. May be installed.

Refractories containing Al ₂ O ₃ and graphite as main components have fine pores which cannot be avoided in the manufacturing process. The presence of the pores also determines the effect of the present invention from the viewpoint of permeation of Ca gas and CO gas. If the porosity is too low, these gases cannot pass through the side wall of the immersion nozzle 6, while if the porosity is too high,
The strength as a refractory decreases and the erosion becomes severe. Therefore, it is preferable that the porosity of the refractory at least inside the slit 7 be 19 to 24% as described above. If the porosity is less than 19%, adhesion of Al ₂ O ₃ occurs, while if the porosity exceeds 24%, erosion of the inner wall of the immersion nozzle occurs.

The molten steel 12 injected from the ladle (not shown) into the tundish 4 is adjusted by the sliding nozzle 5 using the continuous casting equipment having the above-described configuration, and the molten steel outflow holes 21 are adjusted. The discharge flow 16 is injected from the discharge hole 9 into the mold 1 toward the copper plate 3 on the short side of the mold. The poured molten steel 12 is cooled in the mold 1 to form a solidified shell 13, and is continuously drawn out below the mold 1 to form a slab. A mold powder 15 is added onto the molten steel surface 14 in the mold 1 for casting.

During casting, an inert gas such as Ar is supplied into the slit 7 through the gas introduction pipe 11. At that time, the pressure of the inert gas in the slit 7 is maintained higher than the atmospheric pressure. The inert gas pressure in the slit 7 does not need to be particularly limited, and it is sufficient to control the pressure within a range of 5 to 100 kPa higher than the atmospheric pressure.

By casting in this manner, molten steel 12
Even if the Al ₂ O ₃ suspended therein adheres to the inner wall surface of the immersion nozzle 6, the Al ₂ O ₃ changes into a CaO—Al ₂ O ₃ -based low melting point compound, and the inner wall surface of the immersion nozzle 6 Therefore, the growth of the thickness of the Al ₂ O ₃ adhered layer on the inner wall surface of the immersion nozzle 6 is suppressed, and clogging by Al ₂ O ₃ is prevented. As a result, the casting time can be significantly extended. At the same time, since coarsening due to adhesion and deposition of Al ₂ O ₃ particles on the inner wall of the immersion nozzle 6 can be prevented, large inclusions in the slab due to peeling of the coarsened Al ₂ O ₃ can be significantly reduced. Can be reduced.

In the above description, the inert gas is supplied into the slit 7, but the supply of the inert gas is not always necessary.
The hole into which the filler 8 is charged may be closed with a refractory plug or the like, and the slit 7 may be sealed. In the above description, the mold 1 having a rectangular slab cross section has been described. However, the present invention can be applied to a mold having a circular slab cross section. Further, the individual devices of the continuous casting machine are not limited to the above. For example, a stopper may be used instead of the sliding nozzle 5 as a molten steel flow rate adjusting device. Is also good.

[0039]

[Example 1] Using the continuous casting equipment shown in FIGS. 2 and 3, 1-2 m was set near the center of the thickness of the side wall of the immersion nozzle.
A slit having a thickness of about m was provided right above the discharge hole, and a quicklime powder having a particle diameter of 3 mm or less and a graphite powder having a particle diameter of 0.5 mm or less were filled in the slit at a mixing ratio of 1: 1. Casting was performed while supplying Ar into the slit so that the inside of the slit was higher than the atmospheric pressure.
The pressure in the slit was controlled to be 50 to 100 kPa higher than the atmospheric pressure from the beginning to the end of casting. The material of the immersion nozzle was the same as that of the test No. A-2 shown in Table 1 described above. For comparison, casting by an immersion nozzle having no slit was also performed.

The casting conditions were such that 300 tons / heat were continuously cast for 6 heats, and the used immersion nozzle was recovered, and the thickness of the adhered layer adhering to the inside of the slag line was measured in the width direction of the mold and in the direction perpendicular thereto. The thickness of the adhesion layer at the four locations was measured, and the average value was taken as the thickness of the adhesion layer. Cast steel type is low carbon AI killed steel (C: 0.04 to 0.05 mass%, Si:
tr, Mn: 0.1 to 0.2 mass%, Al: 0.03 to
0.04 mass%), and the slab width is 950 to 1200.
mm. The slab drawing speed is 2.2 to 2.
It was 8 m / min.

FIG. 4 shows that the immersion nozzle according to the present invention filled with quicklime powder and graphite powder and the conventional immersion nozzle
_{The 2} O ₃ adhesion thickness is shown for comparison. In the case of the immersion nozzle according to the present invention, adhesion of Al ₂ O ₃ was very small, and further, no solid metal was solidified and adhered to the inner wall surface of the immersion nozzle.

Example 2 Using the continuous casting equipment shown in FIGS. 2 and 3, 1-2 pieces were placed near the center of the thickness of the side wall of the immersion nozzle.
A slit having a thickness of about mm was provided, and a filler was formed at the same blending ratio as in Example 1 using quicklime powder and graphite powder having the same size as in Example 1. Casting was performed while supplying Ar into the slit in the same manner as in Example 1 so that the inside of the slit was higher than the atmospheric pressure. The immersion nozzle material used is the same as in Example 1. However, in this embodiment, the installation range of the slit was changed to six levels from a range from 50 mm from the upper end of the immersion nozzle to a range of 500 mm from the upper end of the immersion nozzle. However, no slit was provided from the upper end of the immersion nozzle to a position 20 mm below. For comparison, casting by an immersion nozzle having no slit was also performed.

After continuous casting at 300 tons / heat for 6 heats, the used immersion nozzle was recovered and the thickness of the adhering layer adhering to the inside of the slag line was measured at four positions in the width direction of the mold and in the direction perpendicular thereto. The thickness of the adhesion layer was measured, and the average value was defined as the thickness of the adhesion layer. Cast steel grade is ultra-low carbon AI killed steel (C: 0.0015 to 0.0025 mass%, Si: t
r, Mn: 0.15 to 0.22 mass%, Al: 0.03
Slab width is 1050 to 1250
mm. The slab drawing speed is 2.2 to 2.
It was 6 m / min.

FIG. 5 shows the relationship between the installation range of the slit, that is, the installation length of the filler, and the thickness of Al ₂ O ₃ adhered. As is clear from FIG. 5, it was found that if the filler is arranged at a position 100 mm below the upper end of the immersion nozzle, the thickness of the Al ₂ O ₃ adhered decreases. This is because the Ca gas and CO gas permeated into the immersion nozzle are carried downstream along with the flow of molten steel, and the thickness of Al ₂ O ₃ adhered to the slag line is reduced. Does not need to be excessively long. Further, in the immersion nozzle, the position immediately below the junction with the sliding nozzle is in the most decompressed state, and it is possible that the installation of the filler in this portion reduces the air passing through the immersion nozzle.

[0045]

According to the present invention, it is possible to suppress the growth of Al ₂ O ₃ deposition layer of immersion nozzle wall, Al ₂
It is possible to prevent the immersion nozzle from being blocked by O ₃ . As a result, the castable time can be significantly extended, and at the same time, defects of large inclusions in the slab due to coarsened Al ₂ O ₃ peeling from the inner wall of the immersion nozzle,
In addition, defects in mold powder property due to drift of molten steel in the mold due to blockage of the immersion nozzle can be significantly reduced, and an industrially advantageous effect is brought about.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a basic experiment performed to elucidate the mechanism of adhesion of Al ₂ O ₃ .

FIG. 2 is a view showing an example of an embodiment of the present invention, and is a schematic diagram of a front vertical cross section of a mold portion of a continuous casting facility.

FIG. 3 is an enlarged view of an immersion nozzle according to the present invention.

FIG. 4 is a diagram showing the results of a survey in Example 1.

FIG. 5 is a diagram showing the results of a survey in Example 2.

[Explanation of symbols]

 Reference Signs List 1 mold 4 tundish 5 sliding nozzle 6 immersion nozzle 7 slit 8 filling 9 discharge hole 10 slag line section 11 gas introduction pipe 12 molten steel 17 upper nozzle 22 high frequency melting furnace 23 chamber 27 test piece holder 28 test piece

Continued on the front page (72) Inventor Hiroshi Awajiya 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Makoto Suzuki 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan F term in the company (reference) 4E004 HA01 MB08 NC01

Claims (6)

[Claims] 1. A continuous casting immersion nozzle for supplying molten steel into a mold, wherein a slit is provided on a side wall thereof, and the slit is filled with a CaO powder and a carbon powder. Immersion nozzle for casting. 2. The immersion nozzle for continuous casting of steel according to claim 1, wherein the slit is shielded from the atmosphere. 3. The immersion nozzle for continuous casting of steel according to claim 1, wherein an inert gas is supplied into the slit, and the inside of the slit is higher than the atmospheric pressure. 4. The method according to claim 1, wherein the particle diameter of the CaO powder is 3 mm or less, and the particle diameter of the carbon powder is 0.5 mm or less. Nozzle for continuous casting of steel. 5. The immersion nozzle inner wall at a portion inside the slit is made of a refractory having a porosity of 19 to 24%. A immersion nozzle for continuous casting of steel according to claim 1. 6. The continuous casting of steel according to claim 1, wherein the slit is provided at least in a range of at least 100 mm below the upper end of the immersion nozzle. Immersion nozzle.