JP2003290887A - IMMERSION NOZZLE FOR CONTINUOUS CASTING AND METHOD FOR CONTINUOUSLY CASTING Al-KILLED STEEL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the clogging an immersion nozzle caused by Al<SB>2</SB>O<SB>3</SB>in molten steel without damaging the cleanliness in a cast slab and also, obstructing the stability of continuous casting operation at the continuous casting of an Al-killed steel. <P>SOLUTION: The immersion nozzle 1 constituted of a refractory material 2 containing ≥5 mass% Ce oxide in the inner hole part 5 contacting with the molten steel is provided. Further, the method for continuously casting the Al- killed steel, with which the molten steel added to at least one kind among metallic Ca, metallic Mg, metallic Ce or the alloy thereof and contained of at least one kind among these elements is poured into a mold through the immersion nozzle constituted of this inner hole part with the refractory material of at least one kind among Ca oxide, Mg oxide and the Ce oxide, is provided with the above state. <P>COPYRIGHT: (C)2004,JPO

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 Al-killed steel and an A nozzle.
The present invention relates to a continuous casting method for l-killed steel, and more specifically to a submerged nozzle and a continuous casting method capable of preventing nozzle clogging of the inner wall of the submerged nozzle due to Al ₂ O ₃ .

[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 mixed with molten steel and Al ₂ O ₃
There is a limit to the floating separation from the molten steel due to the difference in density with 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 being deoxidized in a molten state, and this Al is present in the process of injecting from the ladle into the tundish or in the tundish to the atmosphere. When contacted and oxidized, new Al ₂ O ₃ is formed in the molten steel. These suspended in the molten steel Al ₂ O ₃ is Al ₂
When passing through the dipping nozzle made of O ₃ -graphite, the dipping nozzle adheres and deposits on the inner wall of the dipping nozzle to cause clogging of the dipping nozzle.

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 a method of lowering the melting point of inclusions, there is a method of adding metal Ca to molten steel to modify the form of inclusions from Al ₂ O ₃ to nCaO.mAl ₂ O _3. It is known that the method can prevent nozzle clogging due to Al ₂ O ₃ . However, also in this case, the cleanliness of the slab deteriorates.

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 continuous casting of Al killed steel without impairing the cleanliness of the slab and without hindering the stability of the continuous casting operation. It is an object of the present invention to provide a continuous casting dip nozzle and a continuous casting method that can prevent the above.

[0014]

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.

[Experiment I] As shown in FIG. 1, in the high frequency melting furnace 22 in which the atmosphere in the chamber 23 was adjusted by Ar,
A 1-killed steel was melted and a test piece 28 having a diameter of 25 mm made of an Al ₂ O ₃ -graphitic refractory used as a dipping nozzle material was dipped in the molten steel 12 for 60 minutes. The surface of the test piece 28 was coated with a coating material 29 having a thickness of about 1 mm. The amount of Al ₂ O ₃ adhering to the surface of the test piece 28 after immersion was investigated, and the Al ₂ O ₃ adhesion suppressing effect of the coating material 29 was investigated.

The coating material 29 used is CaO--ZrO.₂ 
-CeO₂ -C quality (partly CeO₂ (Not containing) and MgO
-SiO₂ -CeO₂ -C quality (partly CeO₂ Contain
No.) and the composition was changed to 10.
For comparison, a test without covering with the covering material 29 was also performed.
It was Table 1 shows the composition of the coating material 29 used in the test, and
Al in test piece 28₂ O₃ Shows the adhesion thickness survey results
You In addition, FIG. 1 shows Al₂ O ₃ The basis for elucidating the adhesion mechanism
It is a schematic diagram of the foundation experiment method, and in FIG. 1, 24 is a carp
25, high Al₂ O₃ Quality crucible, 26 thermocouple, 27
Is a test piece holder.

[0017]

[Table 1]

As is apparent from Table 1, the test No. 1 not covered with the coating material was Al ₂ O ₃ in the test No. 2 and the test No. 8 coated with the coating material containing no CeO _2.
The effect of suppressing adhesion is not so remarkable, but CeO ₂ is 5 ma
In all other tests coated with coating material containing more than ss%,
It was found that the Al ₂ O ₃ adhesion thickness is small, and that the addition of 5 mass% or more of Ce oxide has an Al ₂ O ₃ adhesion suppression effect.

Further, CaO-ZrO₂ -CeO₂ -C quality and
MgO-SiO₂ -CeO₂ -C quality and Al₂ O₃ Adhesion
Comparing the suppression effects, as shown in Table 1, the difference between the two is almost
Although it is hardly seen, it has the function of removing sulfur in molten steel.
The contents of aO and MgO differ between the two, CaO-Zr
O₂ -CeO₂ -CaO content is maximum in C-quality coating materials
Judging from the fact that it is 15 mass%, if it is strong, it is Ca
O-ZrO₂ -CeO ₂ -C quality coating material is more Al₂ O
₃ It can be said that the effect of suppressing adhesion is high. In this case, Ca oxide
A and the total compounding amount of Ce oxide are 20 mass% or more.
l₂ O₃ It was found that the effect of suppressing adhesion was particularly large
It was

[Experiment II] Using the high-frequency melting furnace 22 shown in FIG. 1 described above, the molten steel 12 contains metal Ca, metal Mg, and metal C.
Desulfurization by adding e, and the test No. 3 of Experiment I was added to the molten steel.
And coating materials used in Test No. 9 (coat-2 and coat-8)
The test piece 28 coated with is immersed for 60 minutes, and the test piece 28
The amount of Al ₂ O ₃ attached to the surface of the was investigated. In order to confirm the effect of molten steel desulfurization, a test without desulfurizing molten steel was also conducted.

The experimental method is to change the atmosphere in the chamber 23.
About 1.5 kg of Al in the high frequency melting furnace 22 adjusted with Ar
After the killed steel is heated and melted down, the metal C
Addition of a predetermined amount of one or two of a, metal Mg, and metal Ce
After that, the test piece 28 was immersed in the molten steel 12. Melting
Soaking for 60 minutes while maintaining the temperature of Steel 12 at 1580 ° C
Then, the test piece 28 is pulled up and
Al adhering to the surface wall ₂ O₃ The adhesion thickness was investigated. metal
Set of molten steel 12 before adding Ca, metallic Mg, metallic Ce
The composition is C: 0.002 mass%, Mn: 0.20 mass%,
P: 0.010 mass%, S: 0.020 mass%, sol.A
1: adjusted to 0.03 mass%. Table 2 shows the test conditions and tests.
The test results are shown.

[0022]

[Table 2]

As shown in Table 2, the coating thickness of Al ₂ O ₃ on the test piece 28 became almost zero by coating with the coating material and adding a trace amount of the metal Ca, the metal Mg, and the metal Ce to the molten steel. .

Based on the above results, the mechanism of Al ₂ O ₃ adhesion in the immersion nozzle was considered as follows.

Al suspended in molten steel₂ O₃ Particles are soaked
In order to adhere and deposit on the inner wall of the slu₂ O₃ Particles
It is necessary to approach the inner wall of the immersion nozzle.₂ O
₃ In order for particles to remove molten steel and approach the inner wall of the nozzle,
Al₂ O₃ A force is needed to attract the particles. This suction power
The forces that can be considered are the inertial force due to the molten steel flow.
The other is the concentration distribution of sulfur in molten steel near the inner wall.
Is the difference in interfacial tension (Marangoni effect). Real machine
Al on the inner wall of the immersion nozzle used in₂ O₃ Investigation of adhesion status
As a result, the location where the molten steel flow just above the discharge hole stagnates
Al in the (stagnation part) ₂ O₃ Is there a large amount of
Due to the inertia of molten steel₂ O₃ Particles in immersion nozzle
Break through the velocity boundary layer near the wall to reach the inner wall of the nozzle,
It is difficult to think of a mechanism of adhesion and deposition.

By the way, according to the result of Experiment II, when elements such as metal Ca, metal Mg, and metal Ce which generate sulfides are added to the molten steel, the amount of Al ₂ O ₃ deposited becomes small. It can be seen that Al ₂ O ₃ is hard to attach. Also, from the result of Experiment I, the surface of the immersion nozzle was
It has been found that coating with O ₂ , CaO or MgO reduces the amount of Al ₂ O ₃ adhered.

By comparing these phenomena with the distribution of the sulfur concentration near the inner wall of the immersion nozzle, the following can be considered.

When the surface of the immersion nozzle is coated with the coating material used in Test I, the sulfur concentration distribution in the molten steel is low on the inner wall side of the nozzle and high on the molten steel side. The sulfur concentration distribution in the vicinity of the inner wall of the nozzle when coated with the coating material is such that the sulfur in the molten steel is desulfurized by the coating material.

For example, when the surface of the immersion nozzle is coated with a coating material containing CeO ₂ , sulfur in molten steel near the inner wall of the nozzle is desulfurized by the following equations (4) and (5).

[0030]

[Equation 4]

[0031]

[Equation 5]

Due to this desulfurization reaction, the sulfur concentration near the inner wall of the immersion nozzle is lowered, and the concentration gradient of sulfur in the molten steel is low on the nozzle inner wall side and high on the molten steel side. When such sulfur concentration distribution is formed by the difference in sulfur concentration in the case, and Al ₂ O ₃ immersion nozzle side and molten steel side of the particles present are Al ₂ O ₃ particles in the concentration boundary layer, Al ₂ A difference occurs in the interfacial tension between the O ₃ particles and the molten steel, and the difference in the interfacial tension causes Al ₂
The O ₃ particles move away from the inner wall surface of the immersion nozzle so as to repel them. Due to this effect, Al ₂ generated by the equation (4)
O ₃ particles are discharged to the molten steel side, Al ₂ O ₃ particles suspended in the molten steel are also prevented from approaching the inner wall of the nozzle, and Al ₂ O ₃ does not adhere to the inner wall surface of the immersion nozzle. ₂ O
Nozzle blockage due to ₃ is prevented.

Similarly, when the surface of the immersion nozzle is coated with a coating material containing CaO, sulfur in the molten steel is desulfurized because sulfur is dissolved in CaO, and the coating material containing MgO is also coated. In this case, the sulfur in the molten steel is desulfurized by the following equations (6) and (7). Also in these cases, the concentration gradient of sulfur is low on the inner wall side of the nozzle and high on the molten steel side, and Al ₂ O ₃ adhesion to the inner wall surface of the immersion nozzle is suppressed.

[0034]

[Equation 6]

[0035]

[Equation 7]

By the way, since sulfur in molten steel has a surface active property, it is usually unevenly distributed on the inner wall side of the immersion nozzle, and the sulfur concentration on the inner wall side of the nozzle becomes high and becomes low on the molten steel side. or,
When the molten steel solidifies on the inner wall of the immersion nozzle, sulfur as a solute element is distributed to the molten steel side, so that this concentration gradient is promoted. When such sulfur concentration distribution is formed, if the Al ₂ O ₃ particles penetrated into the concentration boundary layer, Al ₂
A difference in the sulfur concentration between the immersion nozzle side of O ₃ particles and the molten steel side causes a difference in the interfacial tension between the Al ₂ O ₃ particles and the molten steel,
Due to this difference in interfacial tension, Al ₂ O ₃ particles are attracted to the inner wall side of the immersion nozzle and are deposited on the inner wall surface of the nozzle.

When the metal Ce and the metal Mg are added to the molten steel and the amount of dissolved oxygen is small like Al killed steel, the sulfur concentration in the molten steel is reduced by the above equations (5) and (7). Further, when the metal Ca is added to the Al killed molten steel, the sulfur concentration in the molten steel is reduced by the following formula (8).

[0038]

[Equation 8]

By these reactions, the sulfur concentration in the molten steel
Is lower, even if sulfur in molten steel is unevenly distributed on the inner wall side of the nozzle.
The gradient of the sulfur concentration distribution near the inner wall of the nozzle becomes gentle,
As a result, Al₂ O₃ Particles are sucked toward the inner wall of the immersion nozzle.
Power is weakened, Al₂ O ₃ Adheres to the inner wall of the nozzle
It gets harder.

The present inventors have found that A on the inner wall of the immersion nozzle
We have come to the conclusions explained above with respect to the l ₂ O ₃ attachment mechanism.

Next, metal Ca, metal Mg, and metal Ce
Addition amount of Al₂ O₃ The effect on adhesion was investigated. test
Is a sulfur concentration in molten steel of 0.005 mass% and 0.020 ma
2 levels of ss% and addition of metal Ca, metal Mg, metal Ce
Perform the same procedure as in Experiment II except that the weights were changed.
I, Al₂ O₃ The adhesion thickness was investigated. And Al₂ O
₃ The amount added was determined so that no adhesion would occur. By the way, metal addition
The sol.Al concentration in the molten steel before was adjusted to 0.03 mass%
Therefore, the equilibrium dissolved oxygen concentration at 1580 ° C is 3 ppm.
Become.

From the test results, when the sulfur concentration in the molten steel before adding the metal is 0.005 mass%, C in the molten steel after the addition is added.
It was found that Al ₂ O ₃ adhesion was prevented by the addition amounts such that a concentration ≧ 0.5 ppm, Mg concentration ≧ 80 ppm, and Ce concentration ≧ 0.1 ppm. When the sulfur concentration in the molten steel before adding the metal is 0.020 mass%, C in the molten steel after the addition is added.
It was found that Al ₂ O ₃ adhesion was prevented by the addition amounts such that the a concentration ≧ 1 ppm, the Mg concentration ≧ 125 ppm, and the Ce concentration ≧ 0.1 ppm.

A regression equation was calculated from these results, and the metal C
The amount of a, metal Mg, and metal Ce to be added depends on the following formula (1) depending on the concentration of sulfur in the molten steel before each addition,
It was found that it is preferable to add so as to satisfy the expressions (2) and (3).

[0044]

[Equation 9]

[0045]

[Equation 10]

[0046]

[Equation 11]

The present invention has been made based on the above test results. The continuous casting immersion nozzle according to the first invention is an immersion nozzle for continuous casting for supplying Al-killed molten steel into a mold, which is in contact with molten steel. The inner hole of the oxide is made of Ce oxide.
It is characterized by being composed of a refractory material containing mass% or more.

In the continuous casting method for Al killed steel according to the second aspect of the present invention, molten steel containing at least one kind of metal Ca, metal Mg, metal Ce or alloys thereof, and containing at least one of these elements. Is injected into the mold through a dipping nozzle whose inner hole is made of a refractory material containing at least one of Ca oxide, Mg oxide and Ce oxide. is there.

The continuous casting method for Al-killed steel according to the third aspect of the present invention is the same as that of the second aspect, wherein the metal Ca, the metal Mg, the metal Ce or their alloys are contained in the molten steel before the addition of these metals or alloys. The Ca concentration (ppm Ca), the Mg concentration (ppm Mg) and the Ce concentration (ppm Ce) after the addition with respect to the sulfur concentration (mass% S) are respectively the above formula (1),
It is characterized in that it is added in a range satisfying the expressions (2) and (3).

A continuous casting method for Al killed steel according to a fourth aspect of the invention is the continuous casting method of the second aspect or the third aspect, wherein the molten steel is blown into the molten steel flowing through the inner hole of the immersion nozzle without introducing Ar into the mold. It is characterized by injecting.

According to the first invention, the immersion nozzle is constructed.
Molten steel sulphurization by Ce oxide contained in refractory materials
Since yellow is desulfurized, the inside of the nozzle will be
The sulfur concentration is low on the wall side and high on the molten steel side.
Al₂ O₃ The particles move to repel the inner wall of the nozzle.
Move. As a result, Al on the inner wall of the immersion nozzle₂ O ₃ 
Adhesion is suppressed.

According to the second aspect of the invention, since the sulfur concentration in the molten steel is lowered by the addition of at least one of metal Ca, metal Mg, metal Ce or alloys thereof, the sulfur concentration distribution in the vicinity of the immersion nozzle can be reduced. Al ₂ O ₃
The suction force on the inner wall of the immersion nozzle for particles is small. In addition, Ca contained in the refractory material forming the immersion nozzle
Since the sulfur in the molten steel is desulfurized by oxide or Mg oxide or Ce oxide, the sulfur concentration is low at the inner wall of the nozzle side in the immersion nozzle near the inner wall, high density distribution molten steel side is formed, Al ₂ O ₃ particles It moves so as to repel from the inner wall of the nozzle. As a result, Al _{2 on the} inner wall of the immersion nozzle
O ₃ adhesion is prevented.

The Al killed steel referred to in the present invention means the steel
The deoxidation product contained in₂ O ₃ Is steel,
Specifically, steel with Al concentration of 0.005 mass% or more
That is.

[0054]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the first embodiment will be described. FIG. 2 is a schematic cross-sectional view of the immersion nozzle according to the present invention, and FIG. 3 is a schematic front vertical cross-sectional view of the mold part of the slab continuous casting equipment used when implementing the present invention.

In the immersion nozzle 1 according to the present invention, at least the portion of the inner hole 5 that comes into contact with the molten steel is composed of a refractory material 2 containing Ce oxide (hereinafter referred to as "containing Ce refractory material 2"). It Although the Ce-containing refractory material 2 is installed only in the vicinity of the inner hole 5 in FIG. 2, all the elements except the slag line portion 4 may be made of the Ce-containing refractory material 2.

The Ce-containing refractory material 2 needs to have a Ce oxide compounding ratio of 5 mass% or more. There is no particular upper limit of the compounding ratio of Ce oxide, but about 20 mass% is sufficient because Ce oxide is expensive and desulfurization of molten steel is saturated. Therefore, as components other than the Ce oxide, CaO, ZrO ₂ , MgO, Al ₂ O ₃ , SiO ₂ ,
One or more kinds of TiO ₂ and C are contained, and C-containing
e Refractory material 2 is constituted. CeO as the Ce oxide
₂ or Ce ₂ O ₃ is used.

Normally, the immersion nozzle for continuous casting of steel is manufactured by using Al ₂ O ₃ -graphite refractory or Al ₂ O ₃ -which has excellent high temperature strength.
It is often composed of SiO ₂ -graphite refractory material. Therefore, as the nozzle base material 3 outside the Ce-containing refractory material 2 shown in FIG. 2, Al ₂ O ₃ -graphite refractory material or Al ₂ O is used. _3-
It is preferable to use SiO ₂ -graphitic refractory. However, the nozzle base material 3 is not limited to these refractory materials, but may be Al ₂ O ₃ -free, SiO ₂ -free, M-free and graphite-free.
A refractory having a gO quality, a ZrO ₂ quality, a Cr ₂ O ₃ quality and a compound composition thereof can be used. Further, the slag line portion 4 provided in the range in contact with the mold powder has excellent corrosion resistance against slag, for example, ZrO ₂ −
Graphite refractory or the like may be used. In the immersion nozzle 1 according to the present invention, it is not always necessary to install the slag line portion 4, but it is preferable to install it from the durability of the immersion nozzle 1.

Using the immersion nozzle 1 having such a configuration, A
The 1-killed molten steel is continuously cast, and as the continuous casting equipment using the immersion nozzle 1 according to the present invention, for example, the continuous casting equipment as shown in FIG. 3 can be used. In FIG. 3, a tundish 10 having a refractory inside is placed above a mold 7 composed of opposing long sides 8 of the mold and opposing short sides 9 of the mold. The upper nozzle 17 is provided at the bottom of the tundish 10, and the sliding nozzle 11 including the fixed plate 18, the sliding plate 19, and the flow control nozzle 20 is connected to the upper nozzle 17 and Further, the immersion nozzle 1 according to the present invention is arranged on the lower surface side of the sliding nozzle 11, and a molten steel supply hole 21 from the tundish 10 to the mold 7 is formed.

Then, the molten steel 12 previously deoxidized with Al in a ladle (not shown) is taken from the ladle to the tundish 10
Further, the molten steel 12 injected into the tundish 10 is passed through the molten steel supply hole 21 while adjusting the molten steel flow rate with the sliding nozzle 11, and the discharge flow 16 is discharged from the discharge hole 6 to the short side 9 of the mold. Inject toward the inside of the mold 7. The poured molten steel 12 is cooled in the mold 7 and solidified shell 1
3 is formed and is continuously drawn out below the mold 7 to form a cast piece. Mold powder 15 is added on the molten steel surface 14 in the mold 7 for casting.

Conventionally, Ar for blowing Al ₂ O ₃ to prevent adhesion of Al ₂ O ₃ is blown into the molten steel 12 flowing down in the molten steel supply hole 21 from any one of the upper nozzle 17, the fixing plate 18, the immersion nozzle 1 or two or more locations. However, when the immersion nozzle 1 according to the present invention is used, it is not necessary to blow Ar for this purpose. If it is to be blown, it is sufficient to blow a very small amount of Ar of about 3 Nl / min.

By continuously casting the molten steel 12 in this way, the concentration of sulfur on the inner wall surface side of the nozzle is low and the concentration of sulfur on the center side of the immersion nozzle 1 is high in the immersion nozzle 1, so that the molten steel 12 and Al ₂ O Difference in interfacial tension between the _three particles,
Al suspended in the molten steel 12 due to this difference in interfacial tension
_{Since 2} O ₃ moves so as to separate from the inner wall surface of the immersion nozzle 1, growth of the Al ₂ O ₃ adhesion layer thickness on the inner wall surface of the immersion nozzle 1 is suppressed and nozzle clogging by Al ₂ O ₃ is prevented. It As a result, it becomes possible to dramatically extend the casting time, and A on the inner wall of the immersion nozzle 1
Since it is possible to prevent the coarsening due to the adhesion and deposition of the l ₂ O ₃ particles, it is possible to significantly reduce the large inclusions in the slab due to the peeling of the coarsened Al ₂ O ₃ .

Next, a second embodiment will be described. FIG. 4 is a schematic view of an immersion nozzle used when carrying out the present invention. The immersion nozzle 1A has the same shape as the immersion nozzle 1 described in the first embodiment, but the inner hole 5 has at least one of Ca oxide, Mg oxide, and Ce oxide. It is composed of a refractory material 2A containing (hereinafter referred to as "Ca-Mg-Ce refractory material 2A").

The Ca-Mg-Ce refractory material 2A has a Ca oxide compounding ratio of 20 when Ca oxide alone is compounded.
mass% or more, when Mg oxide alone is mixed, Mg
If the compounding ratio of the oxide is 50 mass% or more, and if the Ce oxide is compounded alone, the compounding ratio of the Ce oxide is 5 mass% or more. In the case of the compounding compound, if at least one of these conditions is satisfied. good. As long as the compounding ratio does not deviate from the above range, the Ca-Mg-Ce refractory material 2A contains Zr.
_{O 2, SiO 2, Al 2} O 3, can be contained TiO _2, C. The other structure of the immersion nozzle 1A is the same as that of the immersion nozzle 1 shown in FIG. 2, and the same portions are denoted by the same reference numerals, and the description thereof will be omitted.

As the continuous casting equipment used for casting molten steel, for example, the continuous casting equipment in which the immersion nozzle 1A is arranged instead of the immersion nozzle 1 in the continuous casting equipment shown in FIG. 3 can be used.

In the present embodiment, before casting the molten steel 12 in a continuous casting facility, at least one of metal Ca, metal Mg, metal Ce or alloys thereof is added to the molten steel 12 as a desulfurizing agent, Of sulfur is removed beforehand. The lower the sulfur concentration in the molten steel after desulfurization, the better, and 0.005 mass%
The goals are: Therefore, the addition amounts of metal Ca, metal Mg, metal Ce and their alloys are such that the Ca concentration, Mg concentration and Ce concentration after adding these metals and alloys are the sulfur concentrations in the molten steel 12 before adding these. On the other hand, it is preferable to set the ranges so as to satisfy the above expressions (1), (2), and (3), respectively.

The timing of adding these metals and alloys is as follows:
It should be performed after the Al deoxidation of No. 2 is completed, and therefore it may be performed in the ladle or the tundish 10.
As a method of addition, molten metal 1
It is possible to adopt a method in which it is added by blowing it together with a carrier gas from the tip of the lance soaked in 2 or a method in which a wire obtained by coating powder of these metals or alloys with a steel plate or the like is fed into molten steel at a high speed. Although the yield deteriorates, lumps or powders of these metals or alloys may be added directly onto the molten steel 12.

Molten steel 12 to which at least one kind of metal Ca, metal Mg, metal Ce, or an alloy thereof is added.
Is continuously cast in the same manner as the method described in the first embodiment. Also in this case, it is not necessary to blow Ar for preventing Al ₂ O ₃ adhesion into the molten steel 12 flowing down in the molten steel supply hole 21. If it is to be blown, it is sufficient to blow a very small amount of Ar.

In this way, the Al killed steel is continuously cast.
As a result, the concentration of sulfur in molten steel 12 decreases, so
The gradient of the sulfur concentration distribution near the nozzle does not become large,
₂ O ₃ Small suction force on the inner wall of the immersion nozzle for particles
Above, in the immersion nozzle 1A, the sulfur concentration on the inner wall surface side of the nozzle
Is low, the sulfur concentration on the center side of the immersion nozzle 1A is high.
Molten steel 12 and Al₂ O₃ The difference in the interfacial tension between the particles
Occurs, and due to this difference in interfacial tension, Al in molten steel 12₂ O₃ 
Moves so as to separate from the inner wall surface of the immersion nozzle 1A
Therefore, Al on the inner wall surface of the immersion nozzle 1A₂ O₃ Adhesive layer thickness
Growth is suppressed and Al₂ O₃ Prevents nozzle clogging due to
Be stopped. As a result, the casting time has been dramatically extended.
And the A on the inner wall of the immersion nozzle 1A
l₂ O₃ Preventing coarsening due to particle adhesion / accumulation
As a result, coarse Al₂ O ₃ Due to peeling of
The large inclusions in the cast slab can be significantly reduced.

In the above description, the casting mold 7 has a rectangular cross section, but the present invention can be applied to a casting mold having a circular casting cross section. 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 11 as a molten steel flow rate adjusting device. Is also good.

[0070]

EXAMPLES Example 1 Continuous casting of molten steel was performed using the immersion nozzle shown in FIG. 2 in which the Ce-containing refractory material was placed in the inner hole portion and the slab continuous casting machine shown in FIG. . As the Ce-containing refractory material to be installed in the inner hole of the immersion nozzle, CaO-ZrO used as a coating material in Experiment No. 3 of Experiment I was used.
_2- CeO ₂ -C quality (coat-2), Experiment No. 9 of Experiment I
In MgO-SiO ₂ -CeO ₂ -C used as covering material
Two types of quality (coat-8) were used. The thickness of the Ce-containing refractory material is about 5 mm, and the base material of the immersion nozzle is Al ₂ O _3-.
Graphite refractory was used.

Then, molten steel of 300 tons / heat was continuously cast for 3 heats. Since the continuous casting equipment used is a two-strand equipment, one strand used a conventional Al ₂ O ₃ -graphitic refractory immersion nozzle for comparison. In the strand equipped with the immersion nozzle according to the present invention, casting was performed without blowing Ar into the molten steel supply hole from the tundish to the mold, but in the conventional strand equipped with the immersion nozzle, 8Nl / A minute flow rate of Ar was blown.

[0072] after casting, the Al ₂ O ₃ deposition thickness of two locations in the vertical direction directly above the position and the direction of ejection of recovered and immersion nozzle discharge port of the immersion nozzle was measured, and the average value Al ₂ O ₃
The adhesion thickness was used. The cast steel type is ultra low carbon Al killed steel (C: 0.001 to 0.003 mass%, Si: tr, M
n: 0.1 to 0.2 mass%, Al: 0.03 to 0.04
mass%, S: 0.008 to 0.012 mass%),
Slab width is 1200 mm, slab drawing speed is 2.2 m
/ Min.

The Al ₂ O ₃ deposition thickness is CaO--ZrO ₂
-CeO ₂ -C electrolyte (coat-2) in the immersion nozzle arranged containing Ce refractory material of approximately 6mm, MgO-SiO ₂ -Ce
It was about 8 mm in the immersion nozzle in which the Ce-containing refractory material of O ₂ -C quality (coat-8) was arranged. On the other hand, in the case of the conventional immersion nozzle, it is about 16 mm even though Ar is blown, and it is found that the use of the immersion nozzle according to the present invention makes it possible to suppress Al ₂ O ₃ adhesion. It was

Example 2 Continuous casting of molten steel using the immersion nozzle shown in FIG. 4 in which the Ca-Mg-Ce refractory material containing Ca is arranged in the inner hole and the slab continuous casting machine shown in FIG. I went. As the Ca-Mg-Ce refractory material to be installed in the inner hole of the immersion nozzle, C used as a covering material in Experiment No. 2 of Experiment I was used.
aO-ZrO ₂ -C cytoplasm and (coat-1), testing of the experimental I No.
3 CaO-ZrO ₂ was used as the coating material in -CeO ₂ -
C-quality (coat-2), MgO-SiO ₂ -C-quality (coat-7) used as a coating material in Experiment No. 8 of Experiment I, and MgO used as a coating material in Test No. 9 of Experiment I -SiO ₂ -C
Four types of eO ₂ -C quality (coat-8) were used. Containing Ca-Mg-Ce
The refractory materials were all about 5 mm thick, and the base material of the immersion nozzle was Al ₂ O ₃ -graphitic refractory material.

Prior to continuous casting of molten steel, powder of metal Ca, powder of metal Mg and powder of metal Ce were blown into the molten steel in a ladle refining furnace using Ar as a carrier gas. The sulfur concentration in the molten steel before the injection of these powders is 0.008 to 0.0
Since it was 12 mass%, the addition amount of metallic Ca was such that the Ca concentration in the molten steel after addition was 1 ppm, the addition amount of metallic Mg was such that the Mg concentration in the molten steel after addition was 120 ppm, and The amount of Ce added was adjusted and added so that the concentration of Ce in the molten steel after addition was 0.5 ppm.

Then, molten steel of 300 tons / heat was continuously cast for 3 heats. Since the continuous casting equipment used is a 2-strand equipment, each strand contains Ca-Mg-Ce.
The refractory material was changed. At that time, casting was performed without blowing Ar into the molten steel supply hole from the tundish to the mold.

[0077] after casting, the Al ₂ O ₃ deposition thickness of two locations in the vertical direction directly above the position and the direction of ejection of recovered and immersion nozzle discharge port of the immersion nozzle was measured, and the average value Al ₂ O ₃
The adhesion thickness was used. The cast steel type is ultra low carbon Al killed steel (C: 0.001 to 0.003 mass%, Si: tr, M
n: 0.1 to 0.2 mass%, Al: 0.03 to 0.04
mass%), the slab width was 1200 mm, and the slab drawing speed was 2.2 m / min.

The deposited thickness of Al ₂ O ₃ is CaO--ZrO ₂
-CeO ₂ -C electrolyte (coat-2) and MgO-SiO ₂ -C
With an immersion nozzle in which a CaO-Mg-Ce refractory material containing eO ₂ -C (coat-8) is placed, CaO-
The immersion nozzle in which the Ca-Mg-Ce refractory material containing ZrO ₂ -C quality (coat-1) and MgO-SiO ₂ -C quality (coat-7) was arranged had a range of 0 mm to 8 mm.

Al in the case where metal Ca, metal Mg, metal Ce and alloys thereof were not added to the molten steel and a conventional dipping nozzle was used and Ar at a flow rate of 8 Nl / min was blown into the molten steel supply hole from the upper nozzle. ₂ O ₃ adhesion thickness is 15mm-22
It has been empirically confirmed to be mm, and it was therefore found that it is possible to suppress Al ₂ O ₃ adhesion on the immersion nozzle by using the method of the present invention.

[0080]

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 experimental method for elucidating an Al ₂ O ₃ adhesion mechanism.

FIG. 2 is a schematic view of an immersion nozzle according to the present invention.

FIG. 3 is a schematic front vertical cross-sectional view of a mold portion of a slab continuous casting facility used when carrying out the present invention.

FIG. 4 is a schematic view of an immersion nozzle used when carrying out the present invention.

[Explanation of symbols]

1 immersion nozzle 1A immersion nozzle 2 Ce-containing refractory material 2A Ca-Mg-Ce refractory material 3 nozzle base material 4 Slug line section 5 inner hole 6 discharge holes 7 Mold 10 tundish 11 sliding nozzles 12 Molten steel 13 Solidified shell 14 Molten steel surface 15 Mold powder 16 discharge flow

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B22D 41/32 B22D 41/32 41/54 41/54

Claims (4)

[Claims] 1. An immersion nozzle for continuous casting for supplying Al-killed molten steel into a mold, the inner hole portion of which is in contact with the molten steel is made of a refractory material containing 5 mass% or more of Ce oxide. Immersion nozzle for continuous casting. 2. A molten steel containing at least one selected from the group consisting of metal Ca, metal Mg, metal Ce or alloys thereof, and containing at least one of these elements, Ca oxide, M.
A continuous casting method of Al-killed steel, characterized by injecting into a mold through a dipping nozzle whose inner hole portion is made of a refractory material containing at least one of g oxide and Ce oxide. 3. A metal Ca, a metal Mg, a metal Ce or an alloy thereof is added after the addition of the metal concentration (ppm Ca) to the sulfur concentration (mass% S) in the molten steel before the addition of the metal or alloy. ), Mg concentration (ppm Mg) and Ce concentration (pp
m Ce) is the following equation (1), equation (2),
The method for continuous casting of Al-killed steel according to claim 2, wherein the content is added within a range satisfying the expression (3). [Equation 1] [Equation 2] [Equation 3] 4. The continuous casting method of Al-killed steel according to claim 2, wherein Ar is not blown into the molten steel flowing through the inner hole of the immersion nozzle, and the molten steel is injected into the mold. .