JP4213782B2 - Immersion nozzle and continuous casting method of steel using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
[0002]
[Prior art]
FIG. 5 is a schematic explanatory diagram of an immersion nozzle immersed in molten steel in a mold. The lower part of the immersion nozzle 1 is immersed in the molten steel 6 of the mold 5, the molten steel 3 in the tundish 2 flows down the inner surface of the immersion nozzle 1, and discharge flows 4, 4 from the discharge holes provided in the lower part of the immersion nozzle. 'And supplied into the molten steel 6.
[0003]
In the case of the immersion nozzle 1 having a small cross-sectional area of the inner hole, the molten steel fills the inner surface of the immersion nozzle 1 and flows down to the discharge hole by rectification to become the discharge flow 4, 4 ′. Therefore, the flow rates of the discharge flows 4 and 4 ′ are substantially equal and the flow rate is stable. However, during casting of molten steel, foreign substances such as alumina are likely to adhere to the inner surface of the submerged nozzle 1, and when the deposit grows, the inner diameter of the submerged nozzle 1 having a smaller inner cross-sectional area becomes thinner. There is a problem that leads to a blockage accident. In order to prevent the generation and growth of the deposit, argon gas or the like is introduced into the nozzle, but the deposit is not sufficiently prevented.
[0004]
If an immersion nozzle with a sufficiently large cross-sectional area of the inner hole is used, even if deposits are generated on the inner surface of the immersion nozzle 1 during casting of the molten steel, the cross-sectional area of the inner hole is large, so the flow path of the molten steel is sufficient. It is considered that the occurrence of nozzle clogging accidents can be prevented. However, according to the knowledge of the present inventors, in the case of an immersion nozzle having a large cross-sectional area of the inner hole, the molten steel does not fill the immersion nozzle 1 and the meniscus 7 in the immersion nozzle is formed on the inner surface of the immersion nozzle 1. In this case, the portion other than the molten steel flow above the meniscus 7 in the immersion nozzle is filled with argon gas.
[0005]
Since the meniscus 7 in the immersion nozzle is struck by a molten steel flow that flows down from above, it always oscillates. Further, when the argon gas is filled with a large amount, the argon gas pushes down the meniscus 7 in the submerged nozzle and is discharged into the molten steel 6 together with the discharge flow 4, 4 ′. There is a problem that the mold hot water surface 8 is greatly swung. When the argon gas is released, the meniscus 7 in the immersion nozzle moves upward. For this reason, there is a problem that the meniscus 7 in the immersion nozzle always moves up and down.
[0006]
For these reasons, when an immersion nozzle with a large cross-sectional area of the inner hole is used, it is difficult to ensure the rectification of the molten steel on the inner surface of the immersion nozzle, so that the flow rates of the discharge flows 4 and 4 ′ are likely to be uneven. It becomes unstable. FIG. 6 is an explanatory diagram showing an example of a drift index when molten steel is cast at an injection rate of about 5 tons / minute using various immersion nozzles having different inner hole cross-sectional areas. The drift index = (2 | V ₄ −V ′ ₄ |) / (V ₄ + V ′ ₄ ), V ₄ is the discharge speed of the discharge flow 4 in FIG. 5, and V ′ ₄ is the discharge speed of the discharge flow 4 ′. It is.
[0007]
As shown in FIG. 6, in the case of an immersion nozzle having an inner hole cross-sectional area of less than 70 cm ^{2, the} drift index is small and the drift index is stable, but in an immersion nozzle having an inner hole cross-sectional area of 70 cm ² , the drift index is large, As the cross-sectional area is further increased, the drift index tends to be further increased. For example, when the flow rate of the discharge flow 4 in FIG. 5 becomes excessive and reaches the solidified shell 9, nonmetallic inclusions in the molten steel 6 are grasped by the solidified shell 9 and nonmetallic inclusions in the slab are obtained. Since it becomes a thing, it is not preferable. Further, for example, when the flow velocity of the jet flow 4 ′ becomes too low, the flow of the molten steel on the 4 ′ side becomes insufficient, so that the flux 10 on the 4 ′ side is solidified and the solidified flux is caught on the surface of the slab on the 4 ′ side. 4 'side slab surface wrinkles increase.
[0008]
[Problems to be solved by the invention]
Conventionally, in large slab continuous casting, an immersion nozzle having an inner hole cross-sectional area of 50 to 60 cm ² is frequently used. However, as described above, there is a problem that the inner diameter of the immersion nozzle is reduced during the continuous casting operation. . On the other hand, when the inner hole has a cross-sectional area of 70 cm ² or more, the problem that the inner diameter of the nozzle is reduced is solved, but there is a problem that the drift is increased as described above. The present invention solves these problems, and since the inner diameter of the immersion nozzle does not become thin during the continuous casting operation, the desired high-efficiency continuous casting can be performed stably and the drift is small. Therefore, an object of the present invention is to provide an immersion nozzle that can stably slab continuously cast slabs with few non-metallic inclusions and surface defects and that can be immersed in molten steel in a mold.
[0009]
[Means for Solving the Problems]
The present invention relates to (1) a porous refractory for gas suction and a porous refractory for gas suction having a cross-sectional area of the nozzle inner hole of 70 cm ² or more and a pore diameter of 3 to 50 μm arranged on the inner wall surface of the nozzle. An immersion nozzle immersed in molten steel in a mold, comprising a gas suction device having a nozzle inner hole provided with a sealed chamber disposed on the back surface of the nozzle and a gas suction pipe connected to the sealed chamber.
[0010]
(2) The immersion nozzle has left and right openings provided in the side wall near the lower end and a bottom provided with a slit-like opening connecting the left and right openings. It is a structure which discharges molten steel from a part, It is an immersion nozzle as described in said (1) characterized by the above-mentioned.
[0011]
(3) The immersion nozzle according to (1), wherein the immersion nozzle has a structure in which a lower portion thereof is formed in a horizontally wide and divergent shape and a bottom portion is opened, and a molten steel is discharged from the bottom portion. It is.
[0012]
(4) Using the immersion nozzle of (1), (2) or (3) above, sucking the gas in the nozzle inner hole and filling the inner hole with molten steel over the entire length of the nozzle for casting. This is a method for continuous casting of steel.
[0013]
(5) Using the immersion nozzle of (1), (2) or (3), the gas in the nozzle inner hole is sucked to form a meniscus in the immersion nozzle of a desired height in the molten steel in the inner hole of the nozzle. It is a continuous casting method of steel characterized by casting.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory view of an example of an immersion nozzle immersed in molten steel in a mold of the present invention. The immersion nozzle 1 of the present invention is an immersion nozzle used for large slab continuous casting, and has a cross-sectional area S of an inner hole of 70 cm ² or more. A gas suction porous refractory 11 is arranged on the inner wall surface of the nozzle, a sealed chamber 12 is provided on the back surface of the gas suction porous refractory 11, and a gas suction pipe 13 is provided in the sealed chamber 12. It is connected. When the gas in the sealed chamber 12 is sucked by the gas suction pipe 13, the gas in the inner hole of the immersion nozzle 1 is sucked through the gas suction porous refractory 11.
[0015]
As the porous refractory for gas suction of the present invention, a porous refractory having a pore diameter of 3 to 50 μm and the same quality as a conventional porous refractory for gas bubbling can be used. The inventors of the present invention used various porous refractories having different pore sizes as gas refractory porous refractories and reduced the pressure in the nozzle inner hole to 100 PA. FIG. 2 is a diagram showing the depth of penetration of molten steel into the porous refractory at that time. When the pore diameter exceeds 50 μm, the molten steel penetrates into the pores, but when the pore diameter is 50 μm or less, the molten steel does not penetrate into the pores. Therefore, in this invention, it specifies to a refractory with a pore diameter of 50 micrometers or less.
[0016]
In continuous casting, in order to prevent the tundish nozzle from being blocked, an inert gas is often flowed into the immersion nozzle 1 at a rate of 3 N liters / minute or more. In the present invention, the inert gas is sucked, but it is difficult to suck and remove the inert gas with a porous refractory for sucking gas having a pore diameter of 3 μm or less. Therefore, in this application, it specifies to a refractory material of 3 micrometers or more.
[0017]
When the gas in the immersion nozzle hole is sucked and the pressure in the immersion nozzle is reduced, the molten steel 6 in the mold is sucked up due to this pressure reduction and immersed in the immersion nozzle inner hole at a position higher by Hcm than the meniscus 8 in the mold. An in-nozzle meniscus 7 is formed. The meniscus 7 in the immersion nozzle swings because it is struck by the molten steel flow flowing down from above, but if the meniscus 7 in the immersion nozzle is formed at a position where H is sufficiently large, the oscillation of the meniscus 7 in the immersion nozzle is The discharge flows 4 and 4 ′ are not greatly changed, and therefore, the occurrence of uneven flow can be prevented and reduced.
[0018]
In the present invention, an immersion nozzle having a cross-sectional area of the nozzle inner hole of 70 cm ² or more is used. The height H of the meniscus 7 in the sub-nozzle is desired in the immersion nozzle regardless of the cross-sectional area of the nozzle inner hole. By reducing the pressure to a desired value, the desired height can be set. For example, when the pressure in the immersion nozzle is reduced so that the pressure in the immersion nozzle becomes zero, the height H of the meniscus 7 in the immersion nozzle reaches about 1.4 m. On the other hand, in large slab continuous casting, an immersion nozzle having a total length L of 1.4 m or less is often used. Therefore, in this case, the inner hole is filled with the molten steel over the entire length of the immersion nozzle regardless of the cross-sectional area of the immersion nozzle inner hole.
[0019]
As described above, according to the present application, by using an immersion nozzle having a sufficiently large cross-sectional area of the nozzle inner hole, the molten steel is filled over the entire length of the immersion nozzle or the meniscus 7 in the immersion nozzle is formed at a position where H is sufficiently large. And can be cast. The immersion nozzle of the present invention has a sufficiently large cross-sectional area of the nozzle inner hole, so that a flow path of molten steel is ensured even if deposits or the like are generated on the inner wall of the nozzle, thus preventing the immersion nozzle from being blocked. . Further, since the meniscus 7 in the immersion nozzle is formed at a sufficient height that does not cause a large fluctuation in the discharge flow 4, 4 ', or the molten steel is filled over the entire length of the immersion nozzle, casting is performed. Can be prevented and reduced. In the present invention, since the gas in the inner hole of the immersion nozzle is sucked, the gas accumulated in the immersion nozzle does not float as a large bubble from the lower end of the immersion nozzle. There is no significant swing.
[0020]
FIG. 3 is an example of another immersion nozzle according to the present invention, and is an explanatory view of the lower part of the immersion nozzle. FIG. 3A is a front view, and FIG. The immersion nozzle of FIG. 3 has a bottom provided with left and right apertures 14 and 14 ′ provided in a side wall near the lower end, and a slit-like aperture 15 connecting the left and right apertures 14 and 14 ′. This immersion nozzle discharges the molten steel in the nozzle into the mold through the apertures 14 and 14 ′ and the slit-shaped opening 15. When this immersion nozzle is used, the molten steel is also discharged downward from the slit-shaped opening 15, so that the flow of molten steel in the mold is made more uniform than in the case of the immersion nozzle of FIG. 1 without the slit-shaped opening. To do.
[0021]
FIG. 4 is an example of the immersion nozzle of the present invention different from the above, and is an explanatory view of the lower part of the immersion nozzle, (A) is an explanatory view of a roll longitudinal section, and (B) is a longitudinal section of a ha ha. It is explanatory drawing. In other words, the lower part of the immersion nozzle is formed in a downwardly horizontally wide divergent shape with a bottom having no bottom open. In the immersion nozzle of FIG. 4, the molten steel is discharged downward from the bottom of the horizontally long shape along the shape of the inner hole of the mold, but the shape of the discharge hole is close to the shape of the inner hole of the mold for slab casting. The flow of discharged molten steel with respect to the inner wall surface is made more uniform than in the case of the immersion nozzle of FIG.
[0022]
Since the immersion nozzle of FIG. 3 has the slit-shaped opening 15, the total area S ′ of the opening that the molten steel discharges is larger than in the case of FIG. 1. Further, since the molten steel is discharged from the entire bottom surface of the immersion nozzle of FIG. 4, the total area S ′ discharged by the molten steel is larger than that in the case of FIG. When the molten steel flows from the tundish into the immersion nozzle at a rate of M ton / min, the molten steel per unit area of the aperture has an average speed of (M / S 'ton) / min. To discharge. Therefore, when the nozzles of FIGS. 3 and 4 having a large total area S ′ of the hole portion are used, M / S ′ becomes small and the discharge flow rate of the molten steel discharged from the hole portion into the mold becomes small. For this reason, the molten molten steel is prevented from reaching the solidified shell 9 (FIG. 1), and therefore, the nonmetallic inclusions in the molten molten steel are prevented from being caught by the solidified shell 9, and as a result, the casting with less nonmetallic inclusions. A piece is obtained.
[0023]
However, as already described with reference to FIG. 5, when the entire area of the discharge opening is increased, in the conventional immersion nozzle, the height H of the meniscus 7 in the immersion nozzle is reduced and the drift is increased. Will occur.
[0024]
In the present invention, since the gas in the nozzle inner hole is sucked, H can be made sufficiently large. For this reason, the flow velocity of the molten steel discharged into the mold from the aperture can be reduced without generating a drift or the like by using the immersion nozzle of FIGS.
[0025]
【Example】
-1
The present inventors cast molten steel having a carbon content of 0.03% by using the immersion nozzle of the present invention having the structure shown in FIG. The inner hole of the immersion nozzle has an oval shape with a major axis of 120 mm and a minor axis of 90 mm, and a cylindrical shape with a total length of 1200 mm. Openings 14 and 14 'having a diameter of 80 mm and a downward angle of 35 ° are provided on the left and right sides of the lower portion, and slit-shaped openings having a width of 20 mm are provided to connect the openings 14 and 14'.
[0026]
The porous refractory for gas suction used in this immersion nozzle is a cylinder having a pore diameter of 10 μm, a thickness of 10 mm, and a length of 250 mm, and the inner surface of the cylinder extends along the wall surface of the inner hole of the immersion nozzle. Arranged. Gas suction in the inner hole of the immersion nozzle was performed by connecting the suction pipe 13 of FIG. 1 to a vacuum pump and reducing the internal pressure of the sealed chamber 12 to 100 Torr. During casting, the suction of the present invention was switched to the suction of the comparative example, and the molten steel surface in the mold was visually observed. In addition, molten steel was injected into the immersion nozzle at a speed of 1.3 m / min, and argon gas for preventing the tundish nozzle from being blocked was introduced into the immersion nozzle at a rate of 6 N liter / min.
[0027]
In the case of the comparative example in which gas suction is not performed, fluctuations of 10 mm or more in height are always observed on the molten metal surface in the mold, and the inner hole of the immersion nozzle is periodically taken from the molten steel in the mold around the nozzle. Large bubbles that were thought to be caused by the argon gas emitted from the gas were generated. On the other hand, in the case of the present invention in which gas was sucked, the molten metal surface in the mold did not oscillate at all, and bubbles were not generated from the molten steel in the mold.
[0028]
【Example】
-2
The present inventors cast molten steel having a carbon content of 0.03% by using the immersion nozzle of the present invention having the structure shown in FIG. The inner hole of the immersion nozzle has a divergent shape with a width of 500 mm at the lower end, a thickness of 90 mm, and a total length of 1200 mm. The gas suction refractory had a cylindrical shape with a pore diameter of 10 μm, a thickness of 10 mm, and a length of 250 mm, and the cylindrical inner surface was arranged along the wall surface of the inner hole above the immersion nozzle. The gas suction of the inner hole of the immersion nozzle was performed by reducing the internal pressure of the sealed chamber to 100 Torr as in Example 1. During casting, the suction of the present invention was switched to the suction of the comparative example. The immersion nozzle was supplied with molten steel at 1.3 tons / minute in the same manner as in Example 1, and argon gas was introduced at a rate of 6 N liters / minute.
[0029]
When gas suction was not performed, large fluctuations were observed on the molten metal surface in the mold, and large bubbles were intermittently generated from the molten steel in the mold around the nozzle. On the other hand, in the case of the present invention in which gas was sucked, the molten metal surface in the mold did not oscillate at all and no bubbles were generated from the molten steel.
[0030]
【The invention's effect】
Since the immersion nozzle of the present invention has a sufficiently large cross-sectional area of the inner hole, a sufficient flow path for the molten steel is ensured, so that accidents such as immersion nozzle blockage can be effectively prevented. Also, the immersion nozzle of the present invention can stably form a sufficiently high laminar molten steel layer in the inner hole of the immersion nozzle above the discharge hole of the molten steel. Can be prevented. Further, since the total area of the discharge holes of the molten steel is large, the discharge flow rate of the molten steel can be reduced without causing a drift.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an example of an immersion nozzle of the present invention.
FIG. 2 is a graph showing the relationship between the pore diameter of a porous refractory and the maximum molten steel penetration depth.
FIG. 3 is an explanatory diagram of an example of another immersion nozzle of the present invention.
FIG. 4 is an explanatory view of another example of the immersion nozzle of the present invention.
FIG. 5 is a schematic explanatory diagram of a normal immersion nozzle.
FIG. 6 is a diagram of the relationship between the inner hole cross-sectional area of the immersion nozzle and the drift index in a normal immersion nozzle.
[Explanation of symbols]
1: immersion nozzle, 2: tundish, 3: molten steel in tundish, 4, 4 ′: molten steel discharge flow, 5: mold, 6: molten steel in mold, 7: meniscus in immersion nozzle, 8: molten steel meniscus in mold, 9: Solidified shell, 10: Flux, 11: Porous refractory for gas suction, 12: Sealed chamber, 13: Pipe for gas suction, 14: Opening for discharging molten steel, 15: Opening of slit shape for discharging molten steel Department.

Claims (5)

A porous refractory for gas suction having a cross-sectional area of the nozzle inner hole of 70 cm ² or more and a pore diameter of 3 to 50 μm disposed on the inner wall surface of the nozzle, and a sealing disposed on the back surface of the porous refractory for gas suction An immersion nozzle immersed in molten steel in a mold, comprising a gas suction device having a nozzle inner hole provided with a chamber and a gas suction pipe connected to the sealed chamber. The immersion nozzle has left and right openings provided in the side wall near the lower end, and a bottom having a slit-like opening connecting the left and right openings, and molten steel is removed from the opening and the slit-like opening. The immersion nozzle according to claim 1, wherein the nozzle is a structure for discharging. 2. The immersion nozzle according to claim 1, wherein the immersion nozzle has a structure in which a lower portion thereof is formed in a horizontally wide and divergent shape and a bottom portion is opened, and a molten steel is discharged from the bottom portion. Using the immersion nozzle of claim 1 or claim 2 or claim 3 , the gas in the nozzle inner hole is sucked, and the inner hole is filled with molten steel and cast over the entire length of the nozzle, Steel continuous casting method. Using the immersion nozzle according to claim 1, claim 2, or claim 3 , the gas in the nozzle inner hole is sucked, and a meniscus in the immersion nozzle having a desired height is formed in the molten steel in the nozzle inner hole and cast. A continuous casting method for steel.

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