JP2003062645A - Immersion nozzle for continuous casting of steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an immersion nozzle for continuous casting which, at the time of casting steel continuously, makes it possible to prevent blockage due to Al2 O3 in the molten steel without damaging cleanliness of cast iron as well as impairing operational stability of the continuous casting. SOLUTION: The subject is solved by using an immersion nozzle 6 which, in the immersion nozzle for continuous casting to charge molten steel into a casing mold, has a slit 7 on the side wall wherein a filling material 8 consisting of MgO powder, carbon powder and metallic Al powder is charged. At that time, the inside wall of the immersion nozzle at the inner side than the said slit is made of refractory with a porosity being 14-22%. The blockage prevention effect is enhanced by arranging a slit extending at least to a 100-mm lower portion from the top end of the immersion nozzle, making a particle diameter of MgO powder below 3 mm and making a particle diameter of carbon powder below 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 during continuous casting of steel, and more specifically to an immersion nozzle capable of preventing clogging of the immersion nozzle with Al ₂ O _3. It is a thing.

[0002]

2. Description of the Related Art Oxidatively refined molten steel is usually deoxidized by Al to remove oxygen contained in the molten steel increased by the oxidation refining. However, the generated Al ₂ O ₃ particles are
There is a limit to the floating separation from the molten steel due to the difference in density with ₂ O _3, and therefore fine Al ₂ O ₃ particles remain in the molten steel in a suspended state. Further, in order to stably reduce oxygen in the molten steel, Al is present in the molten steel after it is deoxidized, and Al is present. This Al is in contact with the atmosphere in the process of pouring from the ladle into the tundish and in the tundish. When it is oxidized by the above method, Al ₂ O ₃ is newly generated in the molten steel. These Al ₂ O ₃ suspended in molten steel are
When passing through the dipping nozzle made of ₂ O ₃ -graphite, the dipping nozzle adheres to and deposits on the inner wall of the dipping nozzle, and the dipping nozzle is blocked.

When the immersion nozzle is closed, various problems occur in the casting operation and the quality of the slab. For example, not only is the cast strip drawing speed reduced, the productivity is reduced, and in extreme cases, the casting operation itself must be stopped. In addition, Al ₂ O deposited on the inner wall of the immersion nozzle
₃ suddenly exfoliates, becomes large Al ₂ O ₃ particles, and is discharged into the mold, and if these are trapped by the solidification shell in the mold, it becomes a product defect. Molten steel may flow out when it is drawn out and may even lead to a breakout. For this reason, Al ₂ O ₃ adhesion / deposition mechanism on the inner wall of the immersion nozzle and its prevention method have been conventionally studied.

As a conventional Al ₂ O ₃ adhesion mechanism: Al ₂ O ₃ suspended in molten steel collides with the inner wall of the immersion nozzle and is deposited ,: The temperature of the molten steel passing through the immersion nozzle decreases, and The solubility of Al and oxygen in the molten steel decreases, 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, covers the inner wall of the immersion nozzle, and the fine Al ₂ O ₃ particles suspended in the molten steel collide and accumulate on it. Is recommended.

Based on these adhesion and deposition mechanisms: Ar 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. : To prevent the temperature of molten steel on the inner wall side of the submerged nozzle from decreasing, it is covered from the outer wall of the submerged nozzle with a heat insulating sleeve, or in two layers to reduce the amount of heat transfer from the wall of the submerged nozzle, or the heat insulating layer is formed into the meat installed between the thickness: using immersion nozzle of a material with a reduced amount of SiO ₂ as a source of oxygen, Al ₂ O ₃ deposition preventive measures such as suppressing the generation of Al ₂ O ₃ is put forward.

Further, Al ₂ O attached to the inner wall of the immersion nozzle
_As a means for removing ₃ , the material of the immersion nozzle is Al ₂
Including a component that combines with O ₃ to form a low melting point compound,
A measure for preventing Al ₂ O ₃ from adhering to the inner wall of the dipping nozzle to cause Al ₂ O ₃ to flow out as a low melting point compound has also been proposed.

[0007]

However, each of the above countermeasures has the following problems. That is, in the above measures, a part of Ar blown into the immersion nozzle cannot be released 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 trapping, and this becomes a product defect. Further, when trapped in the surface layer of the cast slab, the inner surface of the pores may be oxidized in the continuous casting machine or in the heating furnace before rolling, and this may not be scaled off, resulting in a product defect.

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

In the above measures, S in the material of the immersion nozzle is
Since the iO ₂ decreases, the thermal shock resistance of the immersion nozzle deteriorates. Immersion nozzles are usually used after preheating. This is because refractories are susceptible to thermal shock and crack. SiO ₂
Has an extremely high effect of improving the thermal shock resistance, and by lowering the content of SiO ₂ , the frequency of occurrence of cracks in the immersion nozzle becomes very high immediately after passing the molten steel at the start of casting.

Further, in the above measures, CaO is added as a constituent material of the dipping nozzle so that CaO is added.
And Al ₂ O ₃ are combined to form a low melting point compound,
This low melting point compound can be injected into the mold together with molten steel to prevent Al ₂ O _{3 from} adhering to the inner wall of the immersion nozzle, but because the low melting point compound causing inclusions is allowed to flow into the mold, There is a problem that the cleanliness of the slab deteriorates. Further, the inner wall of the immersion nozzle is worn away, which is not suitable for long-time casting.

As described above, the conventional measures for preventing Al ₂ O _{3 from} adhering can increase the amount of inclusions in the slab or impair the stability of operation even though the clogging of the immersion nozzle can be prevented. , Al ₂ which is satisfactory in all aspects of operation and casting quality
The reality is that 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 with Al ₂ O ₃ in the molten steel during the continuous casting of the molten steel without impairing the cleanliness of the slab and without hindering the stability of the continuous casting operation. It is to provide a dipping nozzle for continuous casting which can be prevented.

[0013]

The present inventors have conducted some basic experiments on the mechanism of Al ₂ O ₃ adhesion in the immersion 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. 1, Al killed steel is melted in a high frequency melting furnace 22 in which the atmosphere in a chamber 23 is adjusted by Ar, and Al ₂ used as a dipping nozzle material is melted in the molten steel 12. A test piece 28 having a diameter of 25 mm made of O ₃ -graphite refractory was immersed. Al ₂ O ₃
-The graphitic refractory has its apparent porosity changed to 5 levels within the range of 12 to 26%. The test piece 28 is provided with a hole having an inner diameter of 10 mm at the axial center thereof, and the particle diameter is within this hole.
MgO powder of 5 to 3 mm and particle diameter of 0.01 to 0.
5mm carbon powder and particle diameter 0.01-0.5mm
And the metal Al powder of No. 2 were filled at a mass ratio of approximately 2: 1: 1. In this basic experiment, magnesia clinker powder was used as MgO powder, graphite powder was used as carbon powder, and commercially available reagent powder was used as metal Al powder. FIG. 1 is a schematic diagram of a basic experimental method for clarifying the Al ₂ O ₃ adhesion mechanism. In FIG. 1, 24 is a coil, 25 is a high Al ₂ O ₃ crucible, and 26 is a thermocouple. .

100 ml of Ar is placed in the hole in which the filler 8 made of MgO powder, carbon powder and metallic Al powder is formed.
/ Min, and the Ar pressure inside the hole is 1 compared to atmospheric pressure.
It was set higher by 5 kPa. Then, after the test piece 28 is immersed for 10 minutes, the pressure in the chamber 23 is reduced to 67.
kPa, held in that state for a total of 60 minutes 12
Then, the test piece 28 was pulled up, and the thickness of the adhered layer and the adhered matter adhered to the outer surface wall of the test piece 28 were identified. The composition of the molten steel 12 is 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 0.013 mass%, Al: 0.06 to 0.
It was in the range of 12 mass%.

For comparison, a solid test piece 28 having no holes was also immersed, and the thickness of the adhering layer and the adhering material adhering to the outer surface wall thereof were identified. In the case of the solid test piece 28, the test piece holder 27 was a solid test piece without holes, and the test piece 28 was immersed without supplying Ar. Table 1 shows the chemical composition and the apparent porosity of the five types of Al ₂ O ₃ -graphitic refractory used as the test piece 28.

[0017]

[Table 1] The test piece 28 is immersed in the molten steel 12 for 60 minutes and then the molten steel 1
Table 1 also shows the measurement results of the thickness of the adhesion layer obtained from the diameter of the test piece 28 taken out from No. 2. As shown in Table 1,
Compared with the case of solid test pieces, the thickness of the deposit is M
It was found that the number of test pieces filled with gO powder, carbon powder and metallic Al powder and supplied with Ar was significantly smaller. Also, this deposit is mainly Al ₂ O ₃ , and
In the case of a test piece filled with MgO powder, carbon powder and metallic Al powder, MgO was formed near the boundary between the body of the test piece and the deposit.
The reaction product of Al ₂ O ₃ with OH was observed.

Further, as shown in Table 1, in the relationship between the thickness of the deposit after immersion for 60 minutes and the apparent porosity of the test piece, the amount of deposition was large when the apparent porosity was 12%, but more pores were found. It was found that the deposit thickness decreased as the apparent porosity increased in the range of porosity. However, the porosity is 24
%, It was observed that the molten steel infiltrated into the pores of the test piece and the test piece became slightly eroded. Therefore, 24%
It has been found that it is dangerous to increase the porosity as described above, and the apparent porosity is preferably in the range of 14 to 22%. or,
From the examination result of the test piece pulled up during the immersion, it was also found that the thickness of the deposit increases in proportion to the immersion time.

Next, a test was conducted in which the compounding ratio of the MgO powder constituting the filler 8 was kept constant at 50 mass% and the compounding ratio of the carbon powder and the metal Al powder was changed, and the particle sizes of the MgO powder, the carbon powder and the metal Al powder were changed. A modified test was performed.

In the test in which the blending ratio of the carbon powder and the metal Al powder was changed, the blending amount of the metal Al powder was 20 to 40 ma.
A total of 7 levels of tests were carried out by changing the range of ss%. In this case, the blending amount of the carbon powder is 30 to 15 mass% according to the blending amount of the metal Al powder, and the Mg content of the metal Al powder is Mg.
The compounding ratio with respect to O powder is 0.59 in terms of molar ratio.
The range is ˜1.18.

In the particle size modification test, the MgO powder had particle diameters of less than 0.5 mm, 0.5 to 3 mm, and 3 mm.
On the other hand, the carbon powder and the metal Al powder have a particle diameter of less than 0.01 mm, 0.01 to 0.5 mm, 0.5 m.
Three levels exceeding m were set, and these were combined and tested.

The test method is the same as the method of investigating the influence of the apparent porosity of the test piece 28. In this case, Al ₂ O
₃ -As a graphite refractory material, test No. A-3 shown in Table 1
The refractory used in 1. was used.

Table 2 shows the test conditions and the measurement results of the thickness of the adhesion layer after the immersion for 60 minutes. Test No. B shown in Table 2
-1 to 7 are tests in which the compounding ratio of the filler was changed,
Test Nos. B-8 and 9 are tests in which the particle diameters of carbon powder and metal Al powder were changed to less than 0.01 mm or more than 0.5 mm, and Test Nos. B-10 and 11 changed the particle diameter of MgO powder. The test was changed to less than 0.5 mm or more than 3 mm.

[0024]

[Table 2] As shown in Table 2, MgO powder, carbon powder, and metallic Al powder
In terms of blending ratio with powder, the blending ratio of metallic Al powder is 20 ma.
ss% (Mole ratio of metal Al powder to MgO powder (below
Below "N_Al/ N_MgO ]) Is 0.59)₂ O
₃ Adhesion was observed, but 23 mass% (N_Al/ N_MgO =
0.67) and above, Al₂ O₃Decrease in adhesion amount
Is seen, and 35 mass% (N_Al/ N_MgO Up to 1.04)
Al₂ O₃The adhered amount of was reduced. However, metal Al powder
The compounding ratio of 35mass% (N_Al/ N _MgO = 1.04)
Al over₂ O₃The effect of suppressing adhesion was saturated. This place
If Al₂ O₃ Carbon powder in the range where the adhesion control effect is maintained
The powder blend ratio is 15 to 2 depending on the metal Al powder blend ratio.
It became 7 mass%. From these results, Al₂ O₃ Adhesion
It is important to mix metal Al powder to suppress
23 mass% (N_Al/ N_MgO = 0.67) or more
I knew that I should do it.

However, the mixing ratio of the metal Al powder is 35 mass.
% (N_Al/ N_MgO = 1.04), Al₂ O₃With
The effect of suppressing adhesion is saturated, and the Al according to the present invention is saturated.
₂ O ₃As will be described later, the effect of suppressing the adhesion of MgO powder is
Based on Mg gas by reaction with metallic Al powder
, Al₂ O₃Demonstrate adhesion control effect for a long time
To achieve this, the molar ratio to the metallic Al powder is 1.5 times (quality).
It is necessary to have about 2.2 times the amount of MgO powder).
In consideration of this point, 23 to 35 mass% metal Al powder is distributed.
It is preferable to combine them. Along with this, blending of carbon powder
The amount is 15 to 27 mass%. MgO powder of metal Al powder
When the blending ratio with respect to the powder is expressed as a molar ratio, N_Al/ N_MgO 
Is preferably in the range of 0.67 to 1.04.

The carbon powder is blended to prevent the oxidation of the metal Al powder during preheating of the immersion nozzle,
If the blending ratio is less than 15 mass%, there is a small amount of carbon powder blended, and there is a concern that oxidation of the metal Al powder cannot be prevented. On the other hand, if the blending ratio exceeds 27 mass%, the amount of metal Al powder to be blended decreases, It becomes difficult to continue generating Mg gas for a long time, and the effect of preventing Al ₂ O ₃ adhesion cannot be maintained for a long time.

Therefore, the MgO powder is set to about 50 mass%,
On the other hand, the mixing ratio of the metal Al powder is 23 to 35 mass.
%, And the blending ratio of carbon powder is preferably 15 to 27 mass%. That is, the mixing ratio of the metal Al powder to the MgO powder is set in the range of 0.67 to 1.04 in terms of molar ratio,
Moreover, it is preferable that the blending ratio of the carbon powder is 15 to 27 mass%.

In a test in which the particle sizes of the MgO powder, the carbon powder and the metal Al powder were changed, the adhesion suppressing effect was remarkable when the carbon powder and the metal Al powder were less than 0.01 mm. On the other hand, when the carbon powder and the metal Al powder exceed 0.5 mm or the MgO powder exceeds 3 mm, A
It was found that the effect of suppressing the adhesion of l ₂ O ₃ was small. This is because the larger the particle size, the less contact with the MgO powder, the metal Al powder and the carbon powder.

The present invention was made based on the above test results. The immersion nozzle for continuous casting of steel according to the first invention is
In a continuous casting dipping nozzle for supplying molten steel into a mold, a mixture of MgO powder, carbon powder and metallic Al powder is arranged inside the side wall thereof. The nozzle according to the third invention is characterized in that, in the first invention, a slit is provided in a side wall of the immersion nozzle, and MgO powder, carbon powder, and metallic Al powder are filled in the slit. In the second aspect of the present invention, the continuous casting immersion nozzle is characterized in that the slit is cut off from the atmosphere.
The immersion nozzle for continuous casting of steel according to the invention of the invention is characterized in that, in the second invention, an inert gas is supplied into the slit, and the inside of the slit is higher than atmospheric pressure.

Further, 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, in which the mixture of the MgO powder, the carbon powder and the metal Al powder is arranged. The inner wall of the submerged nozzle inside the portion is made of a refractory material having a porosity of 14 to 22%, and the submerged nozzle for continuous casting of steel according to the sixth invention is the first invention. To the fifth invention, the mixture of the MgO powder, the carbon powder, and the metal Al powder is at least 100 mm from the upper end of the immersion nozzle.
It is characterized by being installed up to the lower range.
The immersion nozzle for continuous casting of steel according to the invention of any one of the first to sixth inventions, wherein the mixing ratio of the metal Al powder to the MgO powder is 0.67 to a molar ratio.
In the range of 1.04, the blending ratio of the carbon powder is 15 to 27 mass% of the entire mixture, and the immersion nozzle for continuous casting of steel according to the eighth invention is the first invention to the seventh invention. In any one of the inventions, the particle diameter of the MgO powder is 3 mm or less, and the particle diameter of the carbon powder is 0.5 mm or less.

In the present invention, a mixture of MgO powder, carbon powder and metallic Al powder is provided on the side wall of the continuous casting immersion nozzle, or a slit is provided on the side wall of the continuous casting immersion nozzle, and MgO is provided in the slit. Powder, carbon powder and metallic Al powder are filled. The immersion nozzle is heated to about 1200 to 1550 ° C. by the molten steel passing through the immersion nozzle, and the MgO powder placed inside the inner wall of the immersion nozzle,
Carbon powder and metallic Al powder are also heated. Heated M
With gO powder and metal Al powder (often melted),
3MgO (s) + 2Al (l) → Mg (g) + Al ₂ O
The reaction of ₃ (s) occurs, and Mg gas is generated in the side wall of the immersion nozzle.

By the way, the refractory material forming the immersion nozzle usually has a porosity of 10 to 20%. When supplying molten steel into the mold through the dipping nozzle, the sliding nozzle or stopper is used to reduce the cross-sectional area in the middle, that is, the sliding nozzle portion or stopper arm portion is cut more than the dipping nozzle cross-sectional area. Since the area is smaller and the flow rate is controlled, the pressure is always reduced in the immersion nozzle where the molten steel is flowing at a high speed, and the pressure is lower than the atmospheric pressure.

Therefore, the Mg gas generated in the side wall of the immersion nozzle penetrates the side wall of the immersion nozzle and reaches the inner wall surface of the immersion nozzle. Molten steel is present on the inner wall surface side of the immersion nozzle, Mg has a strong affinity with S, and Mg gas reacts with S existing in the boundary layer between the immersion nozzle and molten steel to generate MgS. Therefore, the concentration gradient of S in the molten steel near the inner wall of the immersion nozzle is a reverse gradient, that is, the interface side with the immersion nozzle is low,
Since the S concentration increases toward the molten steel side, there is a difference in the interfacial tension between the Al ₂ O ₃ particles on the immersion nozzle side and the molten steel side, and this difference in the interfacial tension causes the molten steel to approach the inner wall of the immersion nozzle. The Al ₂ O ₃ particles suspended in the sol are repelled from the inner wall of the immersion nozzle. By this effect,
Without adhering Al ₂ O ₃ on the inner wall of the immersion nozzle, Al ₂ O
Nozzle blockage due to ₃ is prevented.

Further, in the case of a normal immersion nozzle in which MgO powder, carbon powder and metallic Al powder are not arranged, the inside of the immersion nozzle is depressurized and the atmosphere permeates the side wall of the immersion nozzle to oxidize molten steel. Al ₂ O ₃ is generated and Al
_{Although it} causes adhesion of ₂ O ₃ , in the immersion nozzle of the present invention, since Mg gas generated inside the immersion nozzle prevents permeation of the atmosphere, adhesion of Al ₂ O ₃ is suppressed also from this viewpoint.

However, when the Mg gas generated in the side wall of the immersion nozzle is brought into contact with the atmosphere, the Mg gas is oxidized to MgO, and the above effect is not exhibited. Therefore, in the present invention, while incorporating carbon powder, further, when the slit is installed, the slit is cut off from the atmosphere, or the inside of the slit is higher than the atmospheric pressure by supplying an inert gas. Thus, the oxidation of Mg gas is prevented.
When an inert gas is supplied into the slit, the inert gas also penetrates 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, which prevents Al ₂ O ₃ from adhering. The effect can be exerted.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION 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, a schematic front vertical cross-sectional view of a mold part of a continuous casting facility, and FIG. 3 is an enlarged view of a dipping nozzle according to the present invention.

As shown in FIG. 2, the inside of the mold 1 is composed of a copper plate 2 on the long side of the mold and a copper plate 3 on the short side of the mold which is installed inside the copper plate 2 on the long side. There is a tundish 4 made of refractory. An upper nozzle 17 is provided at the bottom of the tundish 4, and a fixed plate 18, a sliding plate 19, and an upper nozzle 17 are connected to the upper nozzle 17.
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 refractory submerged nozzle 6 containing as a main component is arranged, 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 MgO is contained in the slit 7.
A filler 8 made of powder, carbon powder and metallic Al powder is formed. Further, a gas introduction pipe 11 for supplying an inert gas such as Ar is connected to the inside of the slit 7. On the outer peripheral portion of the immersion nozzle 6, the slag line portion 1 made of a refractory material having excellent erosion resistance against slag.
0 is provided in a range in contact with the mold powder 15.

The slit 7 can be formed as follows. When molding the dipping nozzle 6, for example, a string-like substance that disappears at the firing temperature is inserted into a predetermined position on the side wall of the dipping nozzle 6, and the substance disappears when the dipping nozzle 6 is fired to form the slit 7. can do.
Further, the filling material 8 is the slit 7 thus formed.
It can be obtained by charging a mixture of MgO powder, carbon powder and metallic Al powder from the outside of the immersion nozzle 6. The filling degree of these powders may be low. The point is that MgO is filled in the slits 7 from the start of casting to the end of casting.
The powder, carbon powder, and metallic Al powder may be charged in such amounts that they are present. As the MgO powder source, magnesia clinker or the like can be used, and as the carbon powder source,
Graphite, charcoal, coke, etc. can be used, and metal A
As the l powder, a commercially available product can be used.

Further, the immersion nozzle 6 is provided without providing the slit 7.
By forming a mixture of MgO powder, carbon powder and metallic Al powder at a predetermined position on the side wall of the dipping nozzle at the time of molding, and by charging the refractory material forming the dipping nozzle 6 around it, the dipping nozzle 6 is molded. A filler 8 made of MgO powder, carbon powder, and metallic Al powder may be placed in the dipping nozzle 6. In this case, the filling 8 is shielded from the atmosphere, and as in the case where the slit 7 is provided, A
It is not necessary to connect the gas introduction pipe 11 for supplying an inert gas such as r.

The mixing ratio of the MgO powder, the carbon powder and the metal Al powder is 0.67 to 1 in terms of molar ratio of the metal Al powder to the MgO powder from the viewpoint of suppressing Al ₂ O ₃ adhesion as described above. It is preferable that the range is 0.04 and the blending ratio of the carbon powder is 15 to 27 mass% of the entire filler 8. Further, the finer the MgO powder, the carbon powder and the metal Al powder, the higher the effect of suppressing the adhesion of Al ₂ O ₃ is. Therefore, the particle diameter of the MgO powder used is 3 mm or less, and the particle diameter of the carbon powder and the metal Al powder is 0.5 mm or less. It is preferable that The particle diameter referred to here is a size that passes through a mesh of 3 mm and a mesh of 0.5 mm, respectively.

The installation range of the filling material 8 is preferably at least the upper end portion 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 adhered can be suppressed by covering the range up to 100 mm below the upper end of the immersion nozzle 6 with the filler 8. This is because the Mg gas that has penetrated into the immersion nozzle 6
It is considered that it is not necessary to lengthen the installation range of the filler 8 because it is carried downstream in the molten steel flow. However, when installing the slit 7, if the slit 7 is installed up to the upper end of the immersion nozzle 6, the strength of the immersion nozzle 6 will be reduced. Therefore, do not install the slit 7 within a range of at least 20 mm from the upper end of the immersion nozzle 6. Is preferred. Similarly, it is desirable to install the slits 7 in the entire circumferential direction of the immersion nozzle 6, but in order to prevent the strength of the immersion nozzle 6 from deteriorating, the range in which the slit 7 is not installed is set in several places in the circumferential direction of the immersion nozzle 6. You may install it.

The refractory material containing Al ₂ O ₃ and graphite as main components has fine pores that cannot be avoided in the manufacturing process. The presence of these pores also affects the effect of the present invention from the viewpoint of Mg gas permeation. If the porosity is too low, the Mg gas cannot pass through the side wall of the dipping nozzle 6, while if the porosity is too high, the strength as a refractory material decreases and melting loss becomes severe. Therefore, it is preferable that the apparent porosity of the refractory material at least inside the portion where the filler 8 is installed is 14 to 22% as described above. If the apparent porosity is less than 14%, Al ₂ O ₃ adheres, while if the apparent porosity exceeds 22%, the inner wall of the immersion nozzle is melted and damaged.

Using the continuous casting equipment configured as described above, the molten steel 12 injected into the tundish 4 from a ladle (not shown) is adjusted by the sliding nozzle 5 while controlling the molten steel flow rate. A discharge flow 16 is injected into the mold 1 from the discharge hole 9 toward the mold short side copper plate 3 via 21. The poured molten steel 12 is cooled in the mold 1 to form a solidified shell 13, which is continuously drawn below the mold 1 to form a slab. Mold powder 15 is added to the molten steel surface 14 in the mold 1 for casting.

During casting, a gas introduction pipe 11 is provided in the slit 7.
An inert gas such as Ar is supplied via At that time, the inert gas pressure in the slit 7 is maintained higher than the atmospheric pressure. The inert gas pressure in the slit 7 is preferably controlled within a range of 5 to 50 kPa higher than the atmospheric pressure. The present inventors have confirmed that the amount of Al ₂ O ₃ adhered can be suppressed by controlling the pressure of the inert gas in the slit 7 within the range. That is, the difference from atmospheric pressure is 5k
If it is less than Pa, there is a concern that air may enter when the Ar pressure fluctuates, while if the difference from the atmospheric pressure exceeds 50 kPa,
It is not preferable because the inner wall of the immersion nozzle is melted.

By casting in this way, the S concentration on the inner wall surface side of the nozzle is low and the S concentration on the center side of the immersion nozzle 6 is high in the immersion nozzle 6, so that the molten steel 12 and Al ₂ O _{3 are}
A difference occurs in the interfacial tension between the particles and the difference in the interfacial tension causes Al ₂ O ₃ suspended in the molten steel 12 to move away from the inner wall surface of the immersion nozzle 6, so that the immersion nozzle 6 Growth of the Al ₂ O ₃ adhesion layer thickness on the inner wall surface is suppressed, and blockage by Al ₂ O ₃ is prevented. As a result, it becomes possible to dramatically extend the casting time,
In addition, since it is possible to prevent coarsening due to adhesion and deposition of Al ₂ O ₃ particles on the inner wall of the immersion nozzle 6, large inclusions in the cast slab caused by the 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, and after charging the filler 8 into the slit 7,
The slit 7 may be sealed by closing the hole into which the filling material 8 is inserted with a plug made of refractory material or the like. Further, in the above description, the mold 1 having a rectangular cast piece cross section has been described, but the present invention can be applied even to a mold having a cast piece cross section of a circular shape. Further, each device of the continuous casting machine is not limited to the above, and any device having the same function may be used, for example, a stopper may be used instead of the sliding nozzle 5 as a molten steel flow rate adjusting device. Is also good.

[0048]

EXAMPLES Example 1 Using the continuous casting equipment shown in FIGS. 2 and 3, a slit having a thickness of 5 mm or less was provided in the vicinity of the center of the thickness of the side wall of the immersion nozzle up to just above the discharge hole, and particles were formed in this slit. Magnesia clinker powder having a diameter of 3 mm or less, graphite powder having a particle diameter of 0.5 mm or less, and metallic Al powder having a particle diameter of 0.5 mm or less were filled at a mass mixing ratio of 2: 1: 1. Further, 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 higher than the atmospheric pressure by 5 to 50 kPa from the beginning to the end of casting. The material of the immersion nozzle is the test No. A shown in Table 1 above.
-3 and the same material. For comparison, casting was also carried out with an immersion nozzle having no slit.

The casting conditions are as follows: 300 tons / heat is continuously cast for 6 heats, the used immersion nozzle is recovered, and the thickness of the adhering layer adhering to the inside of the slag line portion is measured in the mold widthwise position and in the direction perpendicular thereto. The thickness of the adhesive layer was measured at four locations, and the average value was used as the thickness of the adhesive layer. The casting 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.
It was in the range of mm. The slab drawing speed is 2.2-2.
It was 8 m / min.

FIG. 4 shows a comparison of Al ₂ O ₃ adhesion thickness between the immersion nozzle of the present invention filled with magnesia clinker powder, graphite powder and metallic Al powder, and the conventional immersion nozzle. In the case of the immersion nozzle according to the invention, Al ₂ O
₃ Adhesion is extremely small, and further solidification on the inner wall of the immersion nozzle
No attached metal was found.

Example 2 Using the continuous casting equipment shown in FIGS. 2 and 3, 1 to 2 near the center of the wall thickness of the immersion nozzle side wall.
A slit having a thickness of about mm was provided, and a magnesia clinker powder, a graphite powder, and a metal Al powder having the same size as in Example 1 were used to form a filling at the same mixing ratio as in Example 1. Also, so that the inside of the slit is higher than atmospheric pressure,
As in Example 1, casting was performed while supplying Ar into the slit. The material of the immersion nozzle used is the same as in Example 1.
However, in this embodiment, the installation range of the slits was changed to 6 levels from the upper end of the immersion nozzle to 50 mm or from the upper end of the immersion nozzle to 500 mm. However, no slit is provided up to a position 20 mm below the upper end of the immersion nozzle. For comparison, casting was also carried out with an immersion nozzle having no slit.

After continuous casting of 300 tons / heat for 6 heats, the dipping nozzle after use was collected and the thickness of the adhering layer adhering to the inside of the slag line portion was measured at four positions in the mold width direction and the position perpendicular thereto. The adhesion layer thickness was measured, and the average value was taken as the adhesion layer thickness. The cast steel is an 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
〜0.05mass%) and the slab width is 1050 ~ 1250
It was in the range of mm. The slab drawing speed is 2.2-2.
It was 6 m / min.

FIG. 5 shows the relationship between the installation range of the slits, that is, the installation length of the filler and the Al ₂ O ₃ adhesion thickness. As is clear from FIG. 5, it was found that the Al ₂ O ₃ adhesion thickness was reduced if the filler was placed 100 mm below the upper end of the immersion nozzle. This is a result of the Mg gas that has penetrated into the immersion nozzle being carried downstream in the molten steel flow, resulting in a decrease in the Al ₂ O ₃ adhesion thickness in the slag line portion, and the filler installation range is excessive. It means that there is no need to lengthen. Further, in the immersion nozzle, the position immediately below the joint with the sliding nozzle is in the most depressurized state, and the fact that the filler is placed in this part may reduce the atmosphere passing through the immersion nozzle.

[Embodiment 3] Using the continuous casting equipment shown in FIGS. 2 and 3, 1 to 2 are provided near the central portion of the wall thickness of the immersion nozzle.
A slit having a thickness of about mm was provided up to just above the discharge hole, and a magnesia clinker powder, a graphite powder, and a metal Al powder having the same sizes as in Example 1 were used to form a filling at the same mixing ratio as in Example 1. The material used for the immersion nozzle is Example 1
Is the same as However, in this example, the difference between the Ar pressure in the slit and the atmospheric pressure was changed to 8 levels in the range of 0 to 75 kPa.

After continuous casting of 300 tons / heat for 6 heats, the dipping nozzle after use was recovered and the thickness of the adhering layer adhering to the inner side of the slag line portion was measured at four positions in the mold width direction and at a position perpendicular thereto. The adhesion layer thickness was measured, and the average value was taken as the adhesion layer thickness. The casting steel type is a low carbon AI killed steel (C: 0.04 to 0.05 mass%, Si: tr, Mn:
0.1-0.2 mass%, Al: 0.03-0.04 mass
%), And the slab width was in the range of 950 to 1200 mm. Cast strip drawing speed is 2.2 to 2.8 m / min
Met.

FIG. 6 shows the relationship between the difference between the Ar pressure in the slit and the atmospheric pressure and the Al ₂ O ₃ deposition thickness. The vertical axis of FIG. 6 shows the change of the inner diameter of the immersion nozzle, and the increase of the inner diameter represents the melting loss of the inner wall of the immersion nozzle, while the decrease of the inner diameter represents the adhesion of Al ₂ O _3. There is.
As is clear from FIG. 6, it was found that the amount of Al ₂ O ₃ adhered was small in the range where the difference between the Ar pressure in the slit and the atmospheric pressure was in the range of 5 to 55 kPa. On the other hand, the pressure difference is 60
If the pressure exceeds kPa, the inner wall of the immersion nozzle will be melted and damaged.
When the pressure difference was 0, Al ₂ O ₃ adhered.

[0057]

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, it is possible to dramatically extend the castable time, and at the same time, defects in large-scale inclusion physical properties of the slab due to coarse Al ₂ O ₃ peeling from the inner wall of the immersion nozzle,
In addition, it is possible to significantly reduce defects in the mold powder property due to uneven flow of molten steel in the mold due to blockage of the immersion nozzle, which brings an industrially beneficial effect.

[Brief description of drawings]

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

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

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

FIG. 4 is a diagram showing a result of the investigation in Example 1.

FIG. 5 is a diagram showing a result of an examination in Example 2.

FIG. 6 is a diagram showing a result of the investigation in Example 3;

[Explanation of symbols]

1 mold 4 tundish 5 sliding nozzles 6 immersion nozzle 7 slits 8 filling 9 discharge holes 10 Slug line section 11 Gas introduction pipe 12 Molten steel 17 Upper nozzle 22 High frequency melting furnace 23 chambers 27 Test piece holder 28 test pieces

Continued front page    (72) Inventor Makoto Suzuki             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Keiji Watanabe             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F-term (reference) 4K051 AA00 AB03 BE00

Claims (8)

[Claims] 1. A dipping nozzle for continuous casting, wherein a mixture of MgO powder, carbon powder and metallic Al powder is placed inside a side wall of the dipping nozzle for continuous casting for supplying molten steel into a mold. nozzle. 2. A slit is provided on a side wall of the immersion nozzle, and MgO powder, carbon powder, and metal A are provided in the slit.
2. The immersion nozzle for continuous casting of steel according to claim 1, which is filled with 1 powder. 3. The immersion nozzle for continuous casting of steel according to claim 2, wherein the slit is shielded from the atmosphere. 4. The immersion nozzle for continuous casting of steel according to claim 2, wherein an inert gas is supplied into the slit, and the inside of the slit is higher than atmospheric pressure. 5. The inner wall of the immersion nozzle, which is inside the portion where the mixture of MgO powder, carbon powder, and metallic Al powder is arranged, is made of a refractory material having a porosity of 14 to 22%. Claim 1 thru | or Claim 4 characterized by the above-mentioned.
The immersion nozzle for continuous casting of steel according to any one of 1. 6. The mixture of MgO powder, carbon powder and metallic Al powder is at least 10 from the upper end of the immersion nozzle.
The immersion nozzle for continuous casting of steel according to any one of claims 1 to 5, which is installed up to a range below 0 mm. 7. The mixing ratio of the metal Al powder to the MgO powder is 0.67 to 1.04 in terms of molar ratio, and the mixing ratio of the carbon powder is 15 to 27 mass% of the whole mixture.
The immersion nozzle for continuous casting of steel according to any one of claims 1 to 6, wherein 8. The particle diameter of the MgO powder is 3 mm or less, and the particle diameter of the carbon powder is 0.5 mm or less, according to any one of claims 1 to 7. Nozzle for continuous casting of steel.