JP2003290886A - Method for continuously casting steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the clogging of 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 a continuous casting operation at the continuous casting of the steel. <P>SOLUTION: In the continuous casting method for pouring the molten steel 15 in a tundish 13 into a mold 10 through the immersion nozzle 1 disposed at the downstream side of a nozzle gate while controlling the molten steel pouring amount by adjusting the opening degree of the nozzle gate 14, the immersion nozzle constituted of a refractory material containing one or more kinds selected from a group of MgO, carbon, metallic Al, metallic Ti, metallic Zr, metallic Ce and metallic Ca in at least a part thereof is used, and the molten steel is poured in the range of the opening degree of the nozzle gate, with which the pressure in the immersion nozzle becomes lower by ≥346 hPa (0.34 atm) in comparison with the atmospheric pressure. <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 a continuous casting method for steel, and more specifically, to Al ₂ O on the inner wall of the immersion nozzle.
_{The present} invention relates to a continuous casting method capable of preventing blockage due to 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 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.
Its purpose is to prevent the immersion nozzle from being clogged with Al ₂ O _{3 in} molten steel during continuous casting of steel without impairing the cleanliness of the slab and without impairing the stability of the continuous casting operation. It is to provide a continuous casting method capable of performing the same.

[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.

[Basic Experiment] As shown in FIG. 1, Al killed steel is melted in a high frequency melting furnace 31 in which the atmosphere in a chamber 32 is adjusted by Ar, and the molten steel 38 is used as a dipping nozzle material. A test piece 37 made of Al ₂ O ₃ -graphite refractory having a diameter of 25 mm is immersed,
After 15 minutes, 30 minutes, and 45 minutes after dipping the test piece 37, 0.01 mass% of A was added to the molten steel 38, respectively.
1 was added, and 60 minutes after the start of immersion, the test piece 3
7 was pulled up, the thickness of the deposit adhered to the outer surface of the test piece 37 was measured, and the composition of the deposit was identified. The apparent porosity of the Al ₂ O ₃ -graphite refractory used, that is, the test piece 37, was in the range of 12% to 15%.

The composition of the molten steel 38 is C: 0.02 to 0.0.
5 mass%, Si: 0.02 mass% or less, Mn: 0.15
~ 0.20mass%, P: 0.010 ~ 0.016mass
%, S: 0.001 to 0.13 mass%, Al: 0.06
˜0.12 mass%. Incidentally, FIG. 1 is a schematic diagram of a basic experiment method for elucidating the Al ₂ O ₃ adhesion mechanism.
33 is a coil, 34 is a crucible of high Al ₂ O ₃ quality,
Reference numeral 35 is a thermocouple, and 36 is a test piece holder.

Basic Experiment A: Experiments were conducted with and without addition of the surface-active elements sulfur, selenium and tellurium in molten steel, and the effect of surface-active elements on the deposit thickness was investigated. . In this case, experiments were carried out with the sulfur concentration in the molten steel being 0.13 mass%, the selenium concentration being 0.09 mass%, and the tellurium concentration being 0.05 mass%. It is known that the interfacial tension between molten steel containing surface-active elements, such as sulfur, selenium, and tellurium, and Al ₂ O ₃ particles decreases as the concentration of these surface-active elements increases.

The thickness of the deposit after pulling up the test piece is 2 to 3 mm when the sulfur concentration in the molten steel is 0.13 mass%, and 2.5 to 3.6 m when the selenium concentration in the molten steel is 0.09 mass%.
m, 2.8 when the tellurium concentration in the molten steel is 0.05 mass%
It was ~ 3.8 mm, and the thickness of the deposit was extremely thick.
On the other hand, selenium and tellurium are not added, and the molten steel with a sulfur concentration of 0.002 mass% has a deposit thickness of 0.1 to 0.1%.
It was 0.3 mm. The deposits in these experiments were A
It was 1 ₂ O ₃ . In the basic experiment A, the filling substance 39 shown in FIG. 1 was tested without being charged.

Basic experiment B: Inner diameter 1 at the center of the test piece 37
A hole of 0 mm is provided, and MgO powder, carbon powder, metal Al powder, metal Ti is used as a filling material 39 inside the hole.
Powder, metal Zr powder, metal Ce powder, metal Ca powder, or a mixture of two or more of them, and the mixture is filled with MgO.
An experiment was conducted in which the powder was reduced to generate Mg gas, and this Mg gas reduced sulfur in the molten steel at the interface between the test piece 37 and the molten steel 38.

The MgO powder has a diameter of 0.5 mm to 3 mm.
mm magnesia clinker powder, carbon powder is
Using graphite powder having a diameter of 0.01 mm to 0.5 mm, metal Al powder, metal Ti powder, metal Zr powder, metal Ce powder, and metal Ca powder have a diameter of 0.01 mm to.
A commercially available reagent powder of 0.5 mm was used.

Then, MgO powder, graphite powder, and metal A
l powder, metal Ti powder, metal Zr powder, metal Ce powder,
It was filled with one of the metallic Ca powders at a ratio such that the mass ratio was almost equal. That is, graphite powder, metal Al powder, metal T
When one of the i powder, the metal Zr powder, the metal Ce powder, and the metal Ca powder and MgO powder are filled, the mass ratio is 1: 1, and graphite powder, metal Al powder, When two kinds of the metal Ti powder, the metal Zr powder, the metal Ce powder, and the metal Ca powder and the MgO powder are filled, the mass ratio is 1: 1: 1.

In this experiment, the atmospheric pressure in the chamber 32 was set to 1013 hPa (760 torr), 800 hPa (600
torr), 667 hPa (500 torr), 467 hPa (35
It was adjusted to 5 levels of 0 torr and 267 hPa (200 torr), and the amount of the produced Mg gas permeating through the test piece 37 was adjusted. Then, the effect of the amount of Mg gas supplied to the interface between the test piece 37 and the molten steel 38 on the deposit thickness was investigated. In this case, as the atmospheric pressure in the chamber 32 decreases, the amount of Mg gas supplied to the interface between the test piece 37 and the molten steel 38 increases, and the sulfur in the molten steel at the interface decreases. Immediately before the test piece 37 was immersed in the molten steel 38, the sulfur concentration in the molten steel was adjusted to 0.021 mass% in all the tests.

FIG. 2 shows the relationship between the deposit thickness of the test piece 37 and the pressure difference when the filling material 39 is a mixture of MgO powder, carbon powder, and metallic Al powder. However, the pressure difference shown on the horizontal axis of FIG. 2 is the difference between the atmospheric pressure (1013 hPa) and the atmospheric pressure in the chamber 32. As shown in FIG. 2, the larger the pressure difference, the smaller the deposit thickness, and when the pressure difference was 346 hPa (0.34 atm) or more, the deposit thickness was 0.1 mm to 0.6 mm. When the pressure difference was zero or 213 hPa (0.21 atm), the deposit thickness was 1 mm to 1.5 mm. In any case, gas emission from the molten steel surface could not be observed. The main body of the deposit was Al ₂ O ₃ , but MgS and the reaction product of MgO and Al ₂ O ₃ were also observed near the boundary between the test piece 37 and the deposit.

Even when the filling material 39 is composed of one of metal Ti powder, metal Zr powder, metal Ce powder, metal Ca powder and MgO powder and carbon powder instead of metal Al powder, Al powder The thickness of the deposit was reduced as in the case of.

From these results, at least the test piece 37
It was found that the sulfur in the molten steel was removed by the Mg gas at the interface between the molten steel and the molten steel 38, and that the deposit thickness decreased as the sulfur in the molten steel near the interface was removed.

Basic Experiment C: Inner diameter 1 at the center of the test piece 37
A hole of 0 mm is provided, metal Ca or a mixture of metal Ca and carbon powder is filled as a filling substance 39 inside the hole to generate Ca gas, and the Ca gas produces the test piece 3
An experiment was conducted to reduce sulfur in molten steel at the interface between 7 and molten steel 38. In this experiment as well as the basic experiment B, the chamber 32
The inside was decompressed and the amount of Ca gas passing through the test piece 37 was adjusted.

As a result, also in this experiment, by setting the inside of the chamber 32 to 667 hPa (500 torr) or less, that is, the pressure difference is 346 hPa (0.34 atm) or more,
The thickness of the deposit was reduced. In this case, the main component of the deposit was Al ₂ O ₃ , but CaS and the reaction product of CaO and Al ₂ O ₃ were also observed near the boundary between the test piece 37 and the deposit.

As described above, in the basic experiment, the presence of a large amount of surface active elements such as sulfur, selenium and tellurium in molten steel promotes Al ₂ O ₃ adhesion, and
It was found that the removal of the surface-active element sulfur from the interface between the test piece and the molten steel suppressed Al ₂ O ₃ adhesion on the test piece.

From these results, A in the immersion nozzle
The l ₂ O ₃ attachment mechanism was considered as follows. That is, since sulfur in the 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. Further, when 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 Al ₂ O ₃ particles invade the boundary layer in which such a sulfur concentration distribution is formed, due to the difference in sulfur concentration between the immersion nozzle side of the Al ₂ O ₃ particles and the molten steel side, Al ₂ O ₃ particles It is considered that a difference occurs in the interfacial tension with the molten steel, and due to this difference in the interfacial tension, Al ₂ O ₃ particles are attracted to the inner wall side of the immersion nozzle and accumulate on the inner wall surface of the nozzle, causing Al ₂ O ₃ adhesion. It As the content of surface active elements such as sulfur increases, the concentration gradient increases, the Al ₂ O ₃ particles attracted to the inner wall side of the immersion nozzle increase, and the adhesion thickness increases.

On the other hand, when sulfur is removed from the interface between the test piece and the molten steel, the sulfur concentration in the molten steel becomes low on the inner wall side of the nozzle and high on the molten steel side. When such a concentration gradient is formed, the difference in interfacial tension causes the Al ₂ O ₃ particles to separate from the inner wall surface of the immersion nozzle so as to repel them, and to the inner wall surface of the Al ₂ O ₃ particles suspended in the molten steel. Are prevented from approaching, Al ₂ O ₃ does not adhere to the inner wall surface of the immersion nozzle,
It is believed that the nozzle blockage due to Al ₂ O ₃ is prevented.

As described above, the MgO is disposed inside the immersion nozzle, and the MgO is reduced to generate Mg gas.
It has been found that by supplying g gas to the interface between the inner wall of the nozzle and the molten steel, the adhesion of Al ₂ O _{3 on the} immersion nozzle can be prevented. It was also found that Al ₂ O ₃ adhesion could be prevented by disposing metal Ca inside the immersion nozzle. However,
The effect cannot be exhibited unless the generated Mg gas or Ca gas is supplied to the interface.

By the way, the porosity of the refractory material constituting the immersion nozzle is 10% or more, and when injecting the molten steel into the mold through the immersion nozzle, the molten steel supply flow path from the tundish to the mold is used. The installed sliding nozzles and nozzle gates such as stoppers reduce the cross-sectional area in the middle of the molten steel supply passage to adjust the molten steel injection amount. for that reason,
After the cross-sectional area is reduced by the nozzle gate, the pressure inside the molten steel supply channel is reduced and becomes lower than atmospheric pressure. The pressure difference from the atmospheric pressure increases as the opening degree of the nozzle gate decreases.

Therefore, the pressure difference between the pressure in the molten steel supply passage and the atmospheric pressure after the cross-sectional area is reduced by the nozzle gate is 34.
If the opening of the nozzle gate is set to be 6 hPa (0.34 atm) or more, the Mg gas or Ca gas generated inside the side wall of the immersion nozzle passes through the side wall of the immersion nozzle and the inner wall surface of the immersion nozzle. Will be reached. This is also clear from the fact that the rate of gas permeation through the porous material is known to be proportional to the pressure difference between the atmospheres sandwiching the porous material. Therefore, a specific nozzle opening that causes such a pressure difference was calculated.

Considering the pressure change of the molten steel in the molten steel supply passage, the pressure of the molten steel changes abruptly above and below the nozzle gate in the molten steel supply passage, and this pressure difference is obtained by the following equation (1). be able to. However, in the equation (1), ΔP is the pressure difference between the pressure in the molten steel supply channel immediately above the nozzle gate and the pressure in the molten steel supply channel immediately after passing through the nozzle gate, ρ is the molten steel density, g is the gravitational acceleration, A ₁ is the cross-sectional area of the opening of the nozzle gate portion, A ₂ is the cross-sectional area of the molten steel supply passage after the nozzle gate, and V is the linear velocity of the molten steel at the nozzle gate portion. In the present invention, the percentage of the opening cross-sectional area (A ₁ ) of the nozzle gate portion with respect to the cross-sectional area (A ₂ ) of the molten steel supply passage after the nozzle gate is defined as the opening (R) (R = (A ₁ / A ₂ ) × 100).

[0034]

[Equation 1]

In this case, the pressure difference (ΔP) is equal to the atmospheric pressure,
The difference with the pressure in the molten steel supply passage immediately after passing through the nozzle gate matches, and the linear velocity (V) of the molten steel can be calculated by the following equation (2). However, h in the equation (2) is the distance from the nozzle gate to the molten steel surface in the tundish.

[0036]

[Equation 2]

Using the equations (1) and (2), the distance (h)
= 1.3 m, the relationship between the opening (R) and the pressure difference (ΔP) is calculated. When the opening (R) is 20%, the pressure difference (ΔP) is 0.56 atm When the degree (R) is 55%, the pressure difference (ΔP) is 0.34 atm and the opening (R) is 70%.
At this time, the pressure difference (ΔP) is 0.08 atm.

According to the equation (1), if the distance (h) increases and the linear velocity (V) increases, the pressure difference (ΔP) increases even if the opening (R) is constant. On the other hand, in the so-called large tundish which has been used in recent years, the distance (h) is 1.3 m or more. Therefore, when targeting such a large tundish, the opening (R) is set to 55.
% Or less, the pressure difference (ΔP) is at least 0.
You can secure more than 34 atm. The distance (h) is 1.
When it is 3 m or more, the pressure difference (ΔP) can reach only 0.34 atm or more, and never less than that. Therefore, in the present invention, the maximum value of the preferable range of the opening (R) is 55%.
I decided to. However, if the opening (R) is made too small, there is a high risk of nozzle clogging due to solidification of molten steel at the start of casting, so the lower limit of the opening (R) was set to 20%.

The present invention has been made based on the above experimental results. In the steel continuous casting method according to the first invention, the opening of the nozzle gate is adjusted to control the molten steel injection amount, and the downstream of the nozzle gate is controlled. In a continuous casting method of injecting molten steel in a tundish into a mold through a dipping nozzle installed on the side, at least a part of MgO and carbon, metal Al, metal Ti, metal Zr, metal Ce, metal Ca Using an immersion nozzle made of a refractory material containing one or more selected from the group, the opening of the nozzle gate is set to 3 when the pressure in the immersion nozzle is higher than the atmospheric pressure.
It is characterized in that the injection is performed within the range of the opening which becomes lower than 46 hPa (0.34 atm).

In the steel continuous casting method according to the second aspect of the present invention, the molten steel in the tundish is introduced through the immersion nozzle installed on the downstream side of the nozzle gate while adjusting the opening of the nozzle gate to control the molten steel injection amount. In a continuous casting method of injecting into a mold, using an immersion nozzle at least a part of which is made of a refractory material containing metal Ca, the opening of the nozzle gate is compared with the pressure inside the immersion nozzle to atmospheric pressure. It is characterized in that the injection is performed within the range of the opening which becomes lower than 346 hPa (0.34 atm).

In the steel continuous casting method according to the third aspect of the present invention, the molten steel in the tundish is passed through an immersion nozzle installed on the downstream side of the nozzle gate while adjusting the opening of the nozzle gate to control the molten steel injection amount. In a continuous casting method of injecting into a mold, MgO powder and one or more selected from the group consisting of carbon powder, metal Al powder, metal Ti powder, metal Zr powder, metal Ce powder, and metal Ca powder. Using an immersion nozzle having a slit filled with, on the side wall thereof, the opening of the nozzle gate is set such that the pressure inside the immersion nozzle is 346 hPa (0.34 atm) lower than the atmospheric pressure. It is characterized in that it is injected as inside.

In the steel continuous casting method according to the fourth aspect of the present invention, the molten steel in the tundish is passed through an immersion nozzle installed on the downstream side of the nozzle gate while adjusting the opening of the nozzle gate to control the molten steel injection amount. In a continuous casting method of injecting into a mold, using an immersion nozzle having a slit filled with metal Ca powder or metal Ca powder and carbon powder in its side wall, the opening of the nozzle gate, the pressure in the immersion nozzle Is injected within a range of an opening degree that is lower than the atmospheric pressure by 346 hPa (0.34 atm) or more.

A steel continuous casting method according to a fifth invention is characterized in that, in any one of the first invention to the fourth invention, the opening of the nozzle gate is set within a range of 20% to 55%. It is what

In the steel continuous casting method according to the sixth invention, in any one of the first invention to the fifth invention, the molten steel in the mold is blown without injecting an inert gas into the molten steel flowing down in the immersion nozzle. It is characterized by injecting into.

[0045]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. 3, 4 and 5 are schematic views of the immersion nozzle used in carrying out the present invention, and FIG. 6 is
It is a schematic diagram of the front longitudinal section of the mold part of the continuous casting equipment used when carrying out the present invention.

In the present invention, as shown in FIG. 3 and FIG.
Refractory material 2 containing MgO and one or more selected from the group consisting of carbon, metal Al, metal Ti, metal Zr, metal Ce, and metal Ca (hereinafter referred to as “MgO refractory material 2 containing Mg”). 5) or a refractory material 2a containing metal Ca (hereinafter referred to as "Ca-containing refractory material 2a") at least a part of which is used, or as shown in FIG. In addition, MgO powder, carbon powder, metal Al powder, metal Ti powder, metal Zr powder,
Immersion nozzle having a slit 7 filled with one or more selected from the group of metal Ce powder and metal Ca powder as a filling substance 8 (hereinafter referred to as “MgO-containing filling substance 8”) on its side wall. 1, or metal Ca powder or metal Ca powder and carbon powder is cast using a dipping nozzle 1 having a slit 7 filled in as a filling material 8a (hereinafter referred to as "Ca-containing filling material 8a") on its side wall. . A gas introduction pipe 9 for supplying an inert gas such as Ar into the slit 7 is connected to the slit 7.

The slit 7 can be formed as follows. When the immersion nozzle 1 is molded, for example, a string-like substance that disappears at the firing temperature is inserted into a predetermined position on the side wall of the immersion nozzle 1, and the substance disappears when the immersion nozzle 1 is fired to form the slit 7. can do.
Further, the MgO-containing filling substance 8 or the Ca-containing filling substance 8a is loaded with a mixture of MgO powder, carbon powder, metal Al powder, metal Ca powder and the like from the outside of the dipping nozzle 1 in the slit 7 thus formed. It can be obtained by entering. In order to prevent the MgO-containing substance 8 or Ca-containing substance 8a in the slit 7 from being oxidized by the atmosphere, an inert gas such as Ar is supplied from the gas introduction pipe 9 into the slit 7 so that the inside of the slit 7 is at atmospheric pressure. It is preferable to set it higher than. As a matter of course, when the slit 7 is closed, the gas introduction pipe 9 is unnecessary.

MgO-containing refractory material 2 or Ca-containing refractory
When the immersion nozzle 1 is made of the material 2a,
As shown in FIG.
Constructed by refractory material 2 or Ca-containing refractory material 2a
(Referred to as "integral"), or as shown in FIG.
As a result, MgO-containing refractory only in the vicinity of the inner hole 5 that contacts molten steel
Material 2 or Ca-containing refractory material 2a is placed ("Interpolation
It may be called "type"). However, by using the interpolation type,
Al₂ O₃ Not only exerts the anti-adhesion effect of
The strength of the nozzle 1 is improved and the immersion nozzle 1 is handled
And make the usable time equivalent to that of conventional immersion nozzles.
Therefore, it is preferable to use the interpolation type. Also, containing Mg
O refractory material 2 and Ca-containing refractory material 2a are Al₂ O
₃ , SiO ₂ , ZrO₂ , CaO, TiO₂ Kind of young
Alternatively, two or more kinds may be contained. Include these
Thus, the MgO-containing refractory material 2 and the Ca-containing refractory material 2
It is possible to improve the high temperature strength and spalling resistance of a.
Wear.

Usually, the dipping nozzle for continuous casting of steel is made of Al ₂ O ₃ -graphite refractory or Al ₂ O ₃ -which has excellent high temperature strength.
SiO ₂ -graphite refractory is often used, and therefore, as the nozzle base material 3 of the immersion nozzle 1 shown in FIG. 4 and the nozzle base material 3 of the immersion nozzle 1 shown in FIG. 5, Al ₂ O ₃ −
It is preferable to use a graphite refractory or Al ₂ O ₃ —SiO ₂ —graphite refractory. However, the nozzle base material 3 is not limited to these refractory materials, and Al ₂ containing no graphite is used.
O ₃ quality, SiO ₂ quality, MgO quality, ZrO ₂ quality, Cr ₂ O
It can be a refractory having _three materials and their compound composition. Further, as the slag line portion 4 provided in the range in contact with the mold powder, for example, ZrO ₂ -graphite refractory having excellent corrosion resistance against slag may be used. It is not always necessary to install the slag line portion 4 in the immersion nozzle 1, but it is preferable to install it from the durability of the immersion nozzle 1.

In the present invention, continuous casting of molten steel is performed by using the immersion nozzle 1 having such a structure. As a continuous casting facility using such an immersion nozzle 1, for example, continuous casting as shown in FIG. Equipment can be used. Figure 6
In the above, a tundish 13 having a refractory inside is disposed above the mold 10 composed of the opposite mold long sides 11 and the opposite mold short sides 12 provided inside the mold long sides 11. An upper nozzle 20 is provided at the bottom of the tundish 13, and a sliding nozzle 14 composed of a fixed plate 21, a sliding plate 22 and a rectifying nozzle 23 is arranged in connection with the upper nozzle 20. The immersion nozzle 1 described above is arranged on the lower surface side of the sliding nozzle 14, and the tundish 13 to the mold 1 are disposed.
The molten steel supply hole 24 to 0 is formed.

The molten steel 15 injected into the tundish 13 from a ladle (not shown) is passed through the molten steel supply hole 24 while adjusting the molten steel flow rate by the sliding nozzle 14, and is discharged from the discharge hole 6. 19 is poured into the mold 10 toward the mold short side 12. The poured molten steel 15 is cooled in the mold 10 to form a solidified shell 16,
Is continuously pulled out underneath to form a slab. Mold powder 18 is added to the molten steel surface 17 in the mold 10 for casting.

At this time, the opening range (R) of the sliding plate 22 of the sliding nozzle 14 is set such that the pressure inside the immersion nozzle 1 is lower than the atmospheric pressure by 346 hPa (0.34 atm) or more. Inject as. This opening degree (R) can be obtained by the above equation (1) based on the casting conditions and equipment conditions. For example, in the case of a large tundish in which the distance from the upper surface of the sliding plate 22 to the molten steel surface in the tundish 13 is 1.3 m or more, the sliding nozzle 1
If the opening degree (R) of 4 is within the range of 20% to 55%, a predetermined pressure difference can be secured.

In the immersion nozzle 1 during casting, the inner wall surface of the immersion nozzle 1 is heated to about 1500 ° C. and the outer wall surface thereof is heated to about 900 to 1200 ° C. by the molten steel 15 flowing down in the immersion nozzle 1. The part immersed in 15
The temperature is raised to about 40 ° C. Similarly, MgO, carbon, metal Al, metal Ca, etc. arranged inside the immersion nozzle 1 are also heated.

When the MgO-containing refractory material 2 and the MgO-containing filling material 8 are heated to 1300 ° C. or higher, the MgO and the metallic Al in the MgO-containing refractory material 2 and the MgO-containing filling material 8 are heated.
Then, the reaction according to the following equation (3) occurs, and Mg gas is generated in the side wall of the immersion nozzle 1.

[0055]

[Equation 3]

The reduction reaction of MgO represented by the above formula (3) is
The same occurs with carbon, metal Ti, metal Zr, metal Ce, and metal Ca as with metal Al. In addition, metallic Ca not only reduces MgO, but also increases above 1440 ° C.
Since it itself is gasified, the Ca-containing refractory material 2a and the Ca-containing filling substance 8a in the slit 7 are gasified, and Ca gas is generated in the side wall of the immersion nozzle 1. Where carbon is M
In addition to the reduction reaction of gO, it also plays the role of preventing the oxidation of these metals during preheating of the immersion nozzle 1. From this viewpoint, it is preferable to use carbon in combination when using a metal such as metal Al or metal Ca. .

Molten steel 15 is present on the inner wall surface side of the immersion nozzle 1, magnesium and calcium have a strong affinity with sulfur, and Mg gas and Ca gas that have permeated the side wall of the immersion nozzle 1 are inside the immersion nozzle 1. It reacts with the sulfur in the molten steel existing in the boundary layer between the holes 5 and the molten steel 15 to generate MgS and CaS. Therefore, the sulfur concentration in the molten steel near the inner wall of the immersion nozzle becomes low, and the concentration gradient of the sulfur concentration in the molten steel near the inner wall of the immersion nozzle becomes low on the immersion nozzle 1 side and high on the molten steel 15 side. As a result, in the Al ₂ O ₃ particles existing in the boundary layer between the inner wall surface of the immersion nozzle and the molten steel 15, there is a difference in the interfacial tension between the molten steel 15 and the inner wall side of the immersion nozzle. Based on the above, the Al ₂ O ₃ particles separate from the inner wall surface of the immersion nozzle so as to repel them.
Due to this effect, Al ₂ O ₃ is formed on the inner wall surface of the immersion nozzle 1.
Are not adhered, and the nozzle blockage due to Al ₂ O ₃ is prevented.

In the case of the conventional immersion nozzle, the pressure inside the inner hole 5 of the immersion nozzle is reduced so that the atmosphere permeates the side wall of the immersion nozzle to oxidize the molten steel 15 to form Al ₂ O _{3 and} generate Al _{2. Although it} causes ₂ O ₃ adhesion, in the immersion nozzle 1 used in the present invention, the Mg gas and Ca gas generated inside the immersion nozzle 1 hinder the permeation of the atmosphere, and from this point of view also Al ₂ O ₃ adhesion is prevented. To be done.

Conventionally, Ar or the like for preventing Al ₂ O _{3 from} adhering to the molten steel 15 flowing down in the molten steel supply hole 24 from any one of the upper nozzle 20, the fixing plate 21, the dipping nozzle 1 or two or more locations. Although an active gas is blown in, it is not necessary to blow an inert gas for this purpose because the Al ₂ O ₃ adhesion is suppressed when the present invention is carried out. If it is to be blown, a very small amount (3Nl
/ Min) is sufficient. As a result, Ar in the surface layer of the cast slab
Product defects due to inert gas pores such as bubbles can be prevented.

By casting in this way, growth of the thickness of the Al ₂ O ₃ adhesion layer on the inner wall surface of the immersion nozzle 1 is suppressed, and nozzle clogging by Al ₂ O ₃ is prevented. As a result, it becomes possible to dramatically extend the castable time, and 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 1, coarsened Al It is possible to significantly reduce the large inclusions in the cast slab due to the separation of ₂ O ₃ .

In the above description, the casting mold 10 has a rectangular cross section, but the present invention can be applied to a casting mold having a circular 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 14 as a molten steel flow rate adjusting device. Is also good.

[0062]

EXAMPLES Example 1 A continuous casting machine (two-strand continuous casting machine) shown in FIG. 6 was used, and one strand of FIG.
The immersion nozzle (hereinafter referred to as "test nozzle A") shown in Fig. 3 is installed, and the conventional Al ₂ O ₃ -graphite immersion nozzle (hereinafter referred to as "conventional nozzle") is installed on the other strand, Four tons / heat of molten steel was continuously cast.

In the test nozzle A, the nozzle base material was Al ₂ O ₃
-It is made of graphite, and a magnesia clinker powder having a particle diameter of 3 mm or less and a graphite powder and a metal Al powder having a particle diameter of 0.5 mm or less are blended at a blending ratio of 1: 1: 1 inside the graphite. A mixture of these with alumina powder was molded as a MgO-containing refractory material. The MgO refractory material was devised so that the metal Al powder was mixed around the magnesia clinker powder in order to efficiently carry out the reaction between the magnesia clinker powder and the metal Al powder. The reason for mixing the alumina powder is that MgO and Al ₂ O
_This is because spinel is formed by the reaction with ₃ and the strength of the MgO refractory material is increased.

In the injection of Ar into the molten steel supply hole from the tundish into the mold, the test nozzle A did not blow at all during the first two heats, but from the latter two heats to 3 Nl /.
In the conventional nozzle, the flow rate was 10 Nl / min during the entire casting period. Ar was blown from the upper nozzle.

The molten steel depth (h) in the tundish was 1.
Casting was carried out by adjusting the opening angle (R) of the sliding nozzle in the range of 20% to 55% while adjusting it within the range of 3 to 2.0 m. The relationship between the opening (R) of the sliding nozzle and the molten steel injection amount is, for example, when the molten steel height (h) in the tundish is 1.3 m, the opening (R) is 20% and 40%.
% And 60%, the molten steel injection amounts were 3.6 tons / min, 5.1 tons / min, and 6.3 tons / min, respectively, and casting was performed by forming such a conversion table.

As described above, by ensuring the molten steel depth (h) of 1.3 m or more and setting the opening (R) of the sliding nozzle in the range of 20% to 55%, the pressure in the immersion nozzle is Always 346 hPa (0.3
It was kept lower than 4 atm).

The casting steel type is low carbon Al killed steel ((C:
0.04 to 0.05 mass%, Si: tr, Mn: 0.1
~ 0.2 mass%, S: 0.008-0.02 mass%, A
1: 0.03 to 0.04 mass%)), the slab thickness was 220 mm, the slab width was 1600 mm, and the cast strip drawing speed was 1.4 to 2.4 m / min.

[0068] After casting, the inside of the Al ₂ O ₃ deposition thickness of recovery to the discharge hole of the immersion nozzle, was measured at four points in the mold width direction position and its direction perpendicular position, the average value Al ₂ O
_The adhesion thickness was ₃ . As a result, in the test nozzle A, the adhesion thickness was as small as about 5 mm, and no solid metal solidified and adhered to the inner wall surface of the immersion nozzle was observed. On the other hand, in the conventional nozzle, the adhesion of Al ₂ O _{3 having a} thickness of about 15 mm was recognized.

As a result of rolling these cast pieces and finally making them into beverage cans, the number of defective cans produced was 20 to 50 out of 1 million in the cast pieces cast by the conventional nozzle. In the slab cast by the nozzle A, the number of defective cans was 10 or less.

Thus, according to the present invention, the immersion nozzle A
It was confirmed that not only the prevention of l ₂ O ₃ adhesion but also the cleanliness of the slab was enhanced.

Example 2 A continuous casting machine (two-strand continuous casting machine) shown in FIG. 6 was used, and one of the strands was provided with a slitted immersion nozzle (hereinafter referred to as “test nozzle B”) shown in FIG. Installed on the other strand, conventional A
l ₂ O ₃ - immersion nozzle (hereinafter referred to as "conventional nozzle") of graphite was placed and four heats continuously cast molten steel 300 tons / heat.

In the test nozzle B, the nozzle base material was made of Al ₂ O ₃
-Graphite, 5m from the inner hole of the side wall at a position of 5mm
A slit having a thickness of m is provided, and a magnesia clinker powder having a particle diameter of 3 mm or less, a graphite powder having a particle diameter of 0.5 mm or less, and a metal Al powder are 1:
A MgO-containing filling material compounded at a compounding ratio of 1: 1 was inserted. In this case, after the MgO-containing filling material was inserted, the hole into which the MgO-containing filling material was inserted was sealed with a refractory material, and blowing of an inert gas into the slit was stopped. The slit was installed up to the upper end of the discharge hole.

In the injection of Ar into the molten steel supply hole from the tundish into the mold, the test nozzle B did not blow at all during the first two heats, but from the latter two heats to 3Nl /.
In the conventional nozzle, the flow rate was 10 Nl / min during the entire casting period. Ar was blown from the upper nozzle.

The molten steel depth (h) in the tundish was adjusted to approximately 1.8 m, and the opening (R) of the sliding nozzle was adjusted.
Molten steel of 4 heats was cast while maintaining 4 levels of 20%, 40%, 55%, and 80%, respectively. That is, during the casting of 4 heats, casting was performed by adjusting the slab drawing speed so that the opening of the sliding nozzle was almost constant. The relationship between the opening (R) of the sliding nozzle and the molten steel injection amount is, for example, that the molten steel height (h) in the tundish is 1.8.
When m, the opening (R) is 20%, 40%, 60%, 80
%, The molten steel injection rate is 2.8 tons / min,
It was 3.6 tons / minute, 5.5 tons / minute, and 6.5 tons / minute, and such a conversion table was prepared and cast.

The cast steel type is a low carbon Al killed steel ((C:
0.04 to 0.05 mass%, Si: tr, Mn: 0.1
~ 0.2 mass%, S: 0.008-0.02 mass%, A
1: 0.03 to 0.04 mass%)), the slab thickness is 220 mm, the slab width is 1350 mm, and in order to match the molten steel injection amount, the slab drawing speed is 1.2 m / min, respectively. 1.6 m / min, 2.4 m / min,
It was set at 4 levels of 2.8 m / min.

[0076] After casting, the inside of the Al ₂ O ₃ deposition thickness of recovery to the discharge hole of the immersion nozzle, was measured at four points in the mold width direction position and its direction perpendicular position, the average value Al ₂ O
_The adhesion thickness was ₃ . FIG. 7 shows the measurement results of the Al ₂ O ₃ adhesion thickness. In FIG. 7, the shaded areas are the results for the test nozzle B, and the unshaded areas are the results for the conventional nozzle.

As shown in FIG. 7, in the range where the opening (R) is 55% or less, the Al ₂ O ₃ adhesion thickness in the test nozzle B is smaller than that of the conventional nozzle, and casting is hindered. There was no. However, when the opening (R) was 80%, the Al ₂ O ₃ adhesion thickness was about 15 mm for both the test nozzle B and the conventional nozzle, and no significant difference was observed between the two.

As a result of rolling these slabs and finally making them into beverage cans, the number of defective cans produced was 20 to 50 out of 1 million in the slabs cast by the conventional nozzle. In the slab cast by the nozzle B, the number of defective cans was 10 or less. By defect cause, in the case of conventional nozzles,
The defects due to mold powder were 30%, the defects due to Al ₂ O ₃ were 30%, and the rest were unknown. On the other hand, in the case of the test nozzle B, the defects due to the mold powder were zero, the defects due to Al ₂ O ₃ were 80%, and the rest were unknown. Thus, in the casting using the test nozzle B, no defects due to the mold powder were found.

[0079]

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 diagram showing a relationship between a thickness of a deposit and a pressure difference in a basic experiment.

FIG. 3 is a schematic view showing an example of a dipping nozzle used when carrying out the present invention.

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

FIG. 5 is a schematic view showing another example of the immersion nozzle used when carrying out the present invention.

FIG. 6 is a schematic front vertical cross-sectional view of a mold part of a continuous casting facility used when carrying out the present invention.

FIG. 7 is a diagram showing measurement results of Al ₂ O ₃ adhesion thickness in Example 2.

[Explanation of symbols]

1 immersion nozzle 2 MgO-containing refractory material 2a Ca-containing refractory material 3 nozzle base material 4 Slug line section 5 inner hole 6 discharge holes 7 slits 8 MgO-containing filling material 8a Ca-containing filling material 9 gas introduction pipe 10 molds 13 Tundish 14 sliding nozzles 15 Molten steel 16 solidified shell 17 molten steel surface 18 Mold powder 19 discharge flow

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B22D 41/54 B22D 41/54 C04B 35/00 C04B 35/00 W (72) Inventor Makoto Suzuki One in Marunouchi, Chiyoda-ku, Tokyo 1st and 2nd F-term in Nippon Steel Tube Co., Ltd. (reference) 4E014 DA03 DB03 LA01 MA12 MA26 4G030 AA07 AA36 AA60 AA61 AA63 BA30 CA07 GA04 GA19

Claims (6)

[Claims] 1. A continuous casting method of injecting molten steel in a tundish into a mold through an immersion nozzle installed on the downstream side of the nozzle gate while controlling the opening of the nozzle gate to control the molten steel injection amount, At least part of it
Using a dipping nozzle composed of a refractory material containing MgO and one or more selected from the group consisting of carbon, metal Al, metal Ti, metal Zr, metal Ce, and metal Ca, the nozzle comprising: A continuous casting method for steel, characterized in that the opening of the gate is injected within a range of the opening in which the pressure in the dipping nozzle is lower than atmospheric pressure by 346 hPa (0.34 atm) or more. 2. A continuous casting method for injecting molten steel in a tundish into a mold through an immersion nozzle installed on the downstream side of the nozzle gate while controlling the opening of the nozzle gate to control the molten steel injection amount, An immersion nozzle at least a part of which is made of a refractory material containing metallic Ca is used, and the opening of the nozzle gate is lower than the atmospheric pressure by 346 hPa (0.34 atm) or more. The method for continuous casting of steel is characterized in that the injection is performed within the range of the opening degree. 3. A continuous casting method of injecting molten steel in a tundish into a mold through an immersion nozzle installed on the downstream side of the nozzle gate while controlling the opening of the nozzle gate to control the molten steel injection amount, MgO powder and carbon powder,
Metal Al powder, metal Ti powder, metal Zr powder, metal Ce
Powder, one kind or two or more kinds selected from the group of metal Ca powder, and an immersion nozzle having a slit filled with at its side wall, the opening of the nozzle gate, the pressure in the immersion nozzle is atmospheric pressure The method of continuous casting of steel is characterized in that the steel is injected within a range of an opening that is lower than that of 346 hPa (0.34 atm) or more. 4. A continuous casting method of injecting molten steel in a tundish into a mold through an immersion nozzle installed on the downstream side of the nozzle gate while controlling the opening of the nozzle gate to control the molten steel injection amount, Metal Ca powder or metal Ca
Using an immersion nozzle having a slit filled with powder and carbon powder on its side wall, the opening of the nozzle gate is set to 346 hPa (0.3
A continuous casting method for steel, characterized by injecting within a range of an opening that becomes lower than 4 atm). 5. The opening of the nozzle gate is 20% to 5
The method for continuous casting of steel according to any one of claims 1 to 4, characterized in that the content is within the range of 5%. 6. The steel according to claim 1, wherein the molten steel flowing into the immersion nozzle is injected into the mold without blowing an inert gas into the molten steel. Continuous casting method.