JPH11291002A - Immersion nozzle for continuously casting steel and method for continuously casting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an immersion nozzle which can reduce non-metal inclusion and surface crack flaw and is suitable to produce a cast slab having little surface flaw and that a clogging accident hardly causes, and a continuous casting method using this immersion nozzle. SOLUTION: Relating to the immersion nozzle 1 for continuously casting a steel, used by immersing molten steel spouting holes into the molten steel in a mold, a gas exhausting device 11 which forms a meniscus in the immersion nozzle at the upper part of >=100 mm from the molten steel meniscus in the mold by sucking the gas in the immersion nozzle, is arranged at the upper part of >=200 mm from the molten steel spouting holes 6, 6'. This gas exhausting device 11 has the structure wherein a porous cylindrical refractory is arranged along the inner wall surface of the immersion nozzle, and in the gas exhaust device 11, an exhaust gas flow meter and a pressure gage can be arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an immersion nozzle for continuous casting of steel and a continuous casting method.

[0002]

2. Description of the Related Art FIG. 3 is a schematic illustration of a conventional immersion nozzle. In the figure, 1 is a dipping nozzle, 2 is a tundish, 3 is molten steel, 4 is a mold, 5 is a solidified shell, 6 and 6 'are molten steel discharge holes provided in the dipping nozzle, 7 is a meniscus in the dipping nozzle,
8 is the inner hole of the immersion nozzle, 9 is the molten steel meniscus in the mold, 1
0 is the discharge flow of molten steel.

FIG. 3A shows an example of a conventional method in which molten steel discharge holes 6, 6 'are discharge holes having a small sectional area. An example in which molten steel flows from the tundish 2 into the immersion nozzle 1 at a speed of M tons / minute will be described. The total cross-sectional area of the cross-sectional area and 6 'of the discharge holes 6 and S _1. In this case, the molten steel discharge flow 1
The flow rate of 0 is (M / S ₁ ) ton / min, but S ₁ is small due to the small cross-sectional area of 6 and 6 ′, so the discharge flow 10 of molten steel has a high flow rate, for example, reaches the solidified shell 5. .
In this case, the non-metallic inclusions contained in the discharge flow 10 are caught by the solidified shell 5 before moving to the meniscus 9 in the mold.

[0004] Therefore, in the case of Fig. 3A, a slab having many nonmetallic inclusions is obtained. Further, since the discharge flow 10 reaches the solidified shell 5, the growth of the solidified shell 5 becomes unstable and non-uniform, and surface cracks and the like easily occur on the cast slab. Further, there is a problem that the molten steel discharge holes 6, 6 'are so thin that they are easily closed during casting.

FIG. 3B shows another conventional method in which the molten steel discharge holes 6, 6 'have a large cross-sectional area. The total cross sectional area of the discharge hole 6 and 6 'and S _2. The flow rate of the discharge flow 10 of the molten steel in this case becomes a (M / S ₂₎ ton / min, 6 and 6 'is S ₂ is large due to a large cross-sectional area, thus the discharge flow 10 velocity is small. Therefore, the discharge flow 10 does not reach the solidification shell 5. Therefore, it is possible to prevent an increase in non-metallic inclusions in the slab and a generation of cracks on the surface when the discharge flow 10 reaches the solidified shell 5.

As shown in FIG. 3B, in the conventional method, in the case of the molten steel discharge holes 6 and 6 'having a large cross section, the molten steel is not filled in the immersion nozzle, but is inserted into the inner hole of the immersion nozzle 1. Meniscus 7 occurs. The meniscus 7 in the immersion nozzle is oscillating due to being hit by the molten steel flowing down from above, but when the difference H in height between the meniscus 7 in the immersion nozzle and the molten steel meniscus 9 in the mold is small, Due to the swing of the meniscus in the immersion nozzle, a speed difference is generated between the discharge flows 6, 6 ', and as a result, the molten steel meniscus 9 in the mold is formed.
Also rocks. In addition, the inner hole of the immersion nozzle above the meniscus 7 in the immersion nozzle is filled with argon gas for preventing blocking of the tundish nozzle. The filled argon gas intermittently pushes down the meniscus 7 in the immersion nozzle. As a result, large bubbles flow out of the discharge holes, and the molten steel meniscus 9 in the mold is largely swung.

When the molten steel meniscus 9 in the mold oscillates, the surface properties of the slab are greatly impaired. As described above, FIG.
The immersion nozzle (B) is preferable in that the content of nonmetallic inclusions in the slab is small, the occurrence of cracks on the surface of the slab is small, and the immersion nozzle is prevented from being clogged. Is not widely used because it is damaged.

[0008]

DISCLOSURE OF THE INVENTION The present invention is effective in preventing non-metallic inclusions in a slab, reducing the occurrence of cracks on the surface of the slab, effectively preventing blockage of a immersion nozzle, and further impairing the surface properties. An object of the present invention is to provide an immersion nozzle and a continuous casting method using the immersion nozzle, which are suitable for the production of a cast slab that will not be cast.

[0009]

According to the present invention, there is provided (1) a continuous casting immersion nozzle for steel in which a molten steel discharge hole is immersed in molten steel in a mold, wherein the immersion nozzle is at least 200 mm above the molten steel discharge hole. Continuous casting of steel, characterized in that a gas exhaust device for forming a meniscus in the immersion nozzle is arranged in the immersion nozzle 100 mm or more above the molten steel meniscus in the mold by sucking the gas in the immersion nozzle. Immersion nozzle.

(2) The gas exhaust device includes: a porous tubular refractory having an inner surface of the cylinder arranged along the inner wall surface of the immersion nozzle; and a closed chamber disposed on an outer surface of the tubular refractory. A gas exhaust device having a suction pipe connected to the closed chamber, wherein the suction pipe is provided with an exhaust gas flow meter and a pressure gauge indicating the pressure in the closed chamber. It is an immersion nozzle for continuous casting of steel according to 1).

(3) The gas in the immersion nozzle is sucked by using the immersion nozzle for continuous casting of steel according to the above (1) or (2), so that the immersion nozzle is 100% lower than the molten steel meniscus in the mold.
A continuous casting method for steel, characterized in that casting is performed while forming a meniscus in the immersion nozzle in a immersion nozzle having a desired height of not less than mm.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of an example of an immersion nozzle according to the present invention. Each symbol in the figure is the same as in FIG.
1 is an example of a gas exhaust device. The immersion nozzle of the present invention,
This is an immersion nozzle 1 for continuous casting of steel that is used by immersing molten steel discharge holes 6, 6 'in molten steel in a mold 4. In the immersion nozzle 1 of the present invention, the gas exhaust device 11 is disposed on the inner wall surface of the immersion nozzle 200 mm or more above the molten steel discharge holes 6, 6 '. The gas exhaust device 11 sucks the gas in the immersion nozzle, thereby reducing the temperature of the molten steel meniscus 9 in the mold by one.
A meniscus 7 in the immersion nozzle is formed in the immersion nozzle 1 at a height of 00 mm or more.

According to the present invention, the sectional area of the molten steel discharge holes 6, 6 'can be made sufficiently large. Assuming that the sum of the cross-sectional areas of the discharge holes 6 and 6 ′ is S _3, and the casting speed of the molten steel injected from the dish 2 to the immersion nozzle 1 is M ton / min,
The flow rate of the molten steel discharge stream 10 is (M / S ₃ ) ton / min. In this case S ₃ is sufficiently large. Therefore, the flow velocity of the discharge flow 10 is sufficiently slow and does not reach the solidified shell 5,
Therefore, it is possible to prevent an increase in nonmetallic inclusions in the slab and the occurrence of surface cracks. In addition, the discharge holes 6, 6 'have a sufficiently large cross-sectional area and thus are difficult to close.

However, if the sectional area of the molten steel discharge holes 6, 6 'is made sufficiently large without special measures, the structure shown in FIG.
As described in the above, the meniscus 7 in the immersion nozzle approaches the height of the molten steel meniscus 9 in the mold, the difference H in height between the meniscus 7 in the immersion nozzle and the molten steel meniscus 9 in the mold becomes small, and the Oscillation increases and the surface properties of the slab deteriorate. In the present invention, the gas in the immersion nozzle is reduced by suctioning the gas in the immersion nozzle by the gas exhaust device 11, but by reducing the pressure in the immersion nozzle, the molten steel in the mold is sucked into the immersion nozzle and immersed. The meniscus 7 in the nozzle is formed at a position sufficiently higher than the meniscus 9 in the mold.

According to the findings of the present inventors, when the height difference H between the meniscus 7 in the immersion nozzle and the molten steel meniscus 9 in the mold is less than 100 mm, the swing of the molten steel meniscus 9 in the mold is large, and Poor surface properties. Therefore, the exhaust device 11 of the present invention sucks the gas in the immersion nozzle 1 so that H becomes 100 mm or more.

The immersion nozzle is often immersed in the molten steel in the mold at a depth where the discharge holes 6, 6 'are about 100 mm below the molten steel meniscus 9 in the mold and indicated by L in FIG. When the gas exhaust device 11 is arranged at a desired position 200 mm or more above the discharge holes 6 and 6 ′, H + L is 200 mm even if H is 100 mm, so that the gas exhaust device 11 is located above the meniscus 7 in the immersion nozzle. The gas exhaust device 11 having a simple structure can be used.

In FIG. 1, P is the static pressure of the molten steel in the immersion nozzle at the molten steel meniscus 9 in the mold. Although molten steel having a height of H is present in the immersion nozzle above the molten steel meniscus 9 in the mold in FIG. 1, P is kept at approximately 1 atm because the pressure in the immersion nozzle 8 is reduced to less than 1 atm. Te

The meniscus 7 in the immersion nozzle of FIG. 1 also swings because it is struck by the molten steel flowing down from above, but the meniscus 7 in the immersion nozzle is separated from the molten steel meniscus 9 in the mold by a distance H. In addition, the swing of the meniscus 7 in the immersion nozzle is hardly transmitted to the molten steel meniscus 9 in the mold, and the molten steel meniscus 9 in the mold does not swing. Also, even if argon gas for preventing blockage of the tundish nozzle flows into the immersion nozzle, the argon gas that has flowed into the gas exhaust device 1
Since it is discharged at 1, the molten steel meniscus 9 in the mold discharged from the discharge holes 6, 6 'does not swing.

As described above, the immersion nozzle of the present invention can make the cross-sectional area of the molten steel discharge holes 6, 6 'sufficiently large. And the occurrence of surface cracks can be prevented. Although the clogging of the immersion nozzle can be prevented, the use of the immersion nozzle of the present invention further prevents the molten steel meniscus in the mold from swinging, so that a slab having excellent surface properties can be obtained.

FIG. 2 is an explanatory view of another example of the immersion nozzle of the present invention, in which 12 is a porous tubular refractory, 13 is a closed chamber, 1
4 is a suction pipe, 15 is an exhaust gas flow meter, and 16 is a pressure gauge. That is, the gas exhaust device of FIG. 2 includes a porous tubular refractory 12 in which the inner surface of the tube is disposed along the inner wall surface of the immersion nozzle,
It has a closed chamber 13 arranged on the outer surface of the tubular refractory 12 and a suction pipe 14 connected to the closed chamber 13. The suction pipe 14 has an exhaust gas flow meter 15 and a pressure in the closed chamber 13. And a pressure gauge 16 as shown.

In FIG. 1, the gas exhaust device 11 sucks the gas in the inner hole of the immersion nozzle 1. However, since the molten steel flows down into the inner hole of the immersion nozzle 1, the molten steel adheres to the inner wall surface of the immersion nozzle 1. The attached molten steel is easily sucked by the gas exhaust device, and the gas exhaust device 11 is easily clogged. According to the findings of the present inventors, a porous refractory having a pore diameter of 50 μm or less does not enter the pores even if it is sucked when the molten steel adheres to the surface. For this reason, if the porous cylindrical refractory of FIG. 2 is formed of a porous refractory having a pore diameter of 50 μm or less, it is possible to effectively prevent clogging of the gas exhaust device. When using a cylindrical refractory, an airtight chamber is provided on the outer surface of the cylindrical refractory, which is open to the surface of the cylindrical refractory and is closed to the other parts. The gas in the immersion nozzle 1 can be evacuated through the nozzle.

In the present invention, by using the immersion nozzle shown in the example of FIG. 1 or FIG. 2, the gas in the immersion nozzle is sucked into the immersion nozzle having a desired height H 100 mm or more above the molten steel meniscus. Casting is performed while forming a meniscus in the immersion nozzle. The control for forming the meniscus in the immersion nozzle at a desired height H can be performed, for example, by using a thermocouple as a detection end of the meniscus in the immersion nozzle at the height H.

In FIG. 2, the pressure of the inner hole 8 of the immersion nozzle: P _N , the pressure of the closed chamber 13: P _S , the gas suction amount:
Q _N , the area of the porous tubular refractory forming the inner wall surface of the immersion nozzle: A, the thickness of the tubular refractory: L, the permeability of the tubular refractory: K, the molten steel density: ρ, Assuming that the gravitational acceleration is g, if the sectional areas of the discharge holes 6 and 6 ′ are sufficiently large, the following equations (1) and (2) are established.

P _N = P _S + (L · Q _N ) / (A · K) (1) H = P _N / ρ · g (2) From the above equations (1) and (2), the following equation (3) is obtained. In the equation (3), L, A, and K are grasped in advance by the characteristic values of the tubular refractory. Also, ρ. g is a constant.

H = [P _S + (L · Q _N ) / (A · K)] / (ρ · g) (3) Accordingly, Q _N obtained by the exhaust gas flow meter 15 in FIG. Using P _S obtained by the pressure gauge 16, H can be grasped by equation (3).

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors assumed that the inner diameter is 90 mm and the length is
00 mm, the diameter of each of the two discharge holes is 80 mm, and the discharge angle is 45 ° using the immersion nozzle of FIG.
Molten steel of carbon steel having a carbon content of 0.03% was injected into the immersion nozzle at a speed of 1.3 m / min to perform continuous casting. The cylindrical refractory 12 has a pore diameter of 30 μm and a thickness of 10 m.
m, length 100 mm, provided at a position 400 mm above the discharge hole. Ar gas for preventing blockage of the tundish nozzle was flowed into the inner hole of the immersion nozzle 1 at a rate of 6 Nl / min.

[0027] In continuous casting, using a Q _N obtained in the exhaust gas flowmeter 15, the P _S obtained by the pressure gauge 16, by (3), the first half of the casting operation is the H to 200 mm, the casting operation In the latter half, suction in the immersion nozzle was not performed.

When H was set to 200 mm, the molten steel meniscus in the mold did not fluctuate at all, and the surface properties of the obtained cast slab were extremely excellent. When the inside of the immersion nozzle was observed after the completion of casting, the tubular refractory was not clogged and could be used continuously. On the other hand, the molten steel meniscus in the mold when the suction is not performed is always in a oscillating state due to a large fluctuation and a large drift of the discharged molten steel flow, and the Ar gas discharge holes 6 and 6 for preventing the clogging of the tundish nozzle. Large bubbles likely to be caused by the outflow from the ′ were generated intermittently from the molten steel in the mold around the immersion nozzle, causing the molten steel meniscus in the mold to fluctuate greatly. The cast piece cast without suction had double-skinned flaws and had insufficient surface properties.

[0029]

According to the immersion nozzle of the present invention, since the area of the discharge hole can be made sufficiently large, clogging can be sufficiently prevented, and nonmetallic inclusions and surface cracks on the slab can be reduced. However, since the oscillation of the molten steel meniscus in the mold is small, it is possible to manufacture a slab having very few surface flaws.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an example of an immersion nozzle of the present invention.

FIG. 2 is an explanatory view of another example of the immersion nozzle of the present invention.

FIG. 3 is an explanatory view of an example of a conventional immersion nozzle.

[Explanation of symbols]

1: immersion nozzle, 2: tundish, 3: molten steel,
4: Mold, 5: Solidified shell, 6, 6 ': Molten steel discharge hole provided in immersion nozzle, 7: Meniscus in immersion nozzle,
8: inner hole of immersion nozzle, 9: molten steel meniscus in mold, 10: discharge flow of molten steel, 11: gas exhaust device,
12: porous tubular refractory, 13: closed chamber, 14:
Suction tube, 15: exhaust gas flow meter, 16: pressure gauge.

Continuation of the front page (72) Inventor Takahiro Isono 1 Fujimachi, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Hirohata Works

Claims (3)

[Claims] 1. A immersion nozzle for continuous casting of steel which is used by immersing a molten steel discharge hole in molten steel in a mold, wherein the gas in the immersion nozzle is sucked into a immersion nozzle 200 mm or more above the molten steel discharge hole. An immersion nozzle for continuous casting of steel, characterized in that a gas exhaust device for forming a meniscus in the immersion nozzle is disposed in an immersion nozzle at least 100 mm above a molten steel meniscus in a mold. 2. A gas exhaust device, comprising: a porous tubular refractory having an inner surface of a cylinder arranged along an inner wall surface of an immersion nozzle; a closed chamber disposed on an outer surface of the tubular refractory; And a suction pipe connected to the suction pipe, wherein the suction pipe is a gas exhaust device in which an exhaust gas flow meter and a pressure gauge indicating a pressure in the closed chamber are arranged. An immersion nozzle for continuous casting of the described steel. 3. An immersion nozzle having a desired height 100 mm or more higher than a molten steel meniscus in a mold by sucking gas in the immersion nozzle using the immersion nozzle for continuous casting of steel according to claim 1 or 2. A continuous casting method for steel, characterized in that casting is performed while forming a meniscus in a submerged nozzle.