JPH0839214A - Nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To obtain a nozzle excellent in sticking resistance property of inclusion and metal, etc., in molten steel, to prevent the pick-up of carbon in casting of dead soft steel, to improve the quality of the steel and to stabilize the operation by specifying the compositions of an MgO-CaO-SiO2 base composition without containing carbon. CONSTITUTION:The long nozzle is arranged below a ladle lower nozzle A and the long nozzle body 1 is made of an alumina-graphite refractory and a zirconia-graphite refractory 2 is fitted to a slag line and a refractory layer 6 without containing the carbon is arranged on the inner hole surface 3 and the outer periphery 4 at the lower part thereof through a joint filler 5. The refractory layer 6 is composed of the composition of MgO-CaO-SiO2 base, and this composition contains 5-87wt.% CaO, 10-92wt.% MgO and 2-15wt.% SiO2. Therefore, this nozzle is excellent in sticking resistance property since low m. p. compound having the refractoriness resisting to the casting of molten steel and further, the low m. p. of wide liquid phase producing range is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting nozzle which is used by being attached to a ladle, a tundish or the like in continuous casting.

[0002]

2. Description of the Related Art In recent years, with the need for improving the workability of steel sheets for automobiles, tin materials for DI cans, etc., the demands for high purity and high cleanliness of molten steel have become stronger even in the refining of molten steel and the continuous casting process. Has become. At present, in the refining process, prevention of carbon pickup in the continuous casting process has become an important issue with the melting of ultra-low carbon steel.

Further, as measures for reducing inclusions in molten steel, efforts are being made to degas the molten steel and absorb or float inclusions by a weir of the tundish.

In continuous casting, from ladle to tundish,
Alternatively, when sequentially transferring molten steel from the tundish to the mold, nozzles such as a long nozzle, a tundish nozzle, and a dipping nozzle are used. An alumina / graphite refractory having excellent corrosion resistance and spalling resistance is used for this nozzle.

In the alumina / graphite nozzle, nozzle clogging often occurs due to precipitation / adhesion of inclusions in the steel during casting of molten steel, and particularly precipitation / adhesion of alumina inclusions in casting of aluminum killed steel is remarkable. Occurrence of nozzle clogging disturbs the molten steel flow in the mold and causes deterioration of quality due to entrainment of the flux for continuous casting, and the number of continuous castings decreases, leading to a decrease in production efficiency.

The inclusions are removed by blowing Ar gas into the nozzle in order to prevent the nozzles from being clogged by the inclusions. On the other hand, the surface of the steel due to the inclusion of powder due to the blowing of the Ar gas. There are also defects.

It is considered that nozzle clogging due to inclusions, particularly nozzle clogging due to alumina inclusions, occurs as follows.

That is, (1) aluminum in steel forms alumina by secondary oxidation such as oxidation by air and oxidation by oxygen supplied by oxidation / reduction reaction with silica in refractory. (2) This alumina diffuses and aggregates,
Alumina clusters are formed. (3) Carbon disappears on the operating surface of the nozzle, and the surface becomes uneven.
(4) In the molten steel flow near the operating surface of this nozzle,
There is a stagnation with no flow velocity of 50 to 100 μm, and alumina clusters adhere to the inner wall surface due to the difference in specific gravity from the molten steel or the physical adhesion force. (5) A liquid phase of oxides (MnO, SiO ₂ , CaO, MgO, etc.) in molten steel adheres between the clusters, and the alumina cluster layer is formed by using this as a bond, and the alumina cluster layer gradually becomes thicker. ,
Nozzle is blocked.

In order to prevent the nozzle clogging of such a continuous casting nozzle, Japanese Patent Laid-Open No. 165548/56,
JP-A-57-383668, JP-A-57-563
No. 77 publication discloses a nozzle for continuous casting using a lime / carbon brick. The lime component of this lime / carbonaceous continuous casting nozzle reacts with alumina precipitated from molten steel to cause CaO.Al ₂ O ₃ and 3CaO.Al ₂
It is said that a low-melting-point substance such as O ₃ is generated and flows without staying on the inner wall of the nozzle, which has an effect of preventing nozzle clogging.

However, the inclusion of inclusions due to the formation of the CaO--Al ₂ O ₃ -based low-melting point substance is prevented at 1500 ° C.
Since the liquid phase generation region in the vicinity is narrow, the liquid phase is limited to the region where the amount ratio of CaO and Al ₂ O ₃ is approximately 1: l. Even if the anti-adhesion effect is exhibited, the nozzle begins to adhere with the passage of time and finally the nozzle is clogged.

Further, a refractory composition in which the surface oxidation resistance is improved without impairing the spalling resistance and erosion resistance of the alumina / graphite material is disclosed in Japanese Patent Publication No. 49-480.
As is known from Japanese Patent Publication No. 47, it is difficult to form a low-melting substance, it is inferior in the effect of preventing inclusions from inclusions, and gas is generated from calcium carbonate, which deteriorates the structure of the construction body. Moreover, since the construction thickness is thin, there is a drawback that the duration is short. Further, the alumina / graphite nozzle contains about 20 to 30% by weight of a proper graphite for improving spalling resistance. 40 by volume ratio
%, And it is widely exposed on the operation side. In the casting of molten steel, carbon on the nozzle operating surface is taken into the molten steel due to wear or reaction with oxygen in the molten steel. The refining technology in recent years has made it possible to melt single ppm-order ultra-low carbon steel, and it has become essential to prevent carbon big-up even in the continuous casting process. Carbon-free materials such as refractory materials for steelmaking, refractory materials for TD, and powder for continuous casting are being promoted.
There is also a strong need for carbonless graphite nozzles.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is that it has excellent resistance to inclusions in molten steel, metal ingots, etc., and also prevents carbon pickup in the casting of ultra-low carbon steel, thus improving the quality of steel. , A nozzle for continuous casting that stabilizes the operation, especially a composition that forms a liquid phase during use, further lowers the melting point and melts due to reaction with alumina and Fe oxide, and does not easily deposit inclusions in molten steel To provide a nozzle for continuous casting.

[0013]

DISCLOSURE OF THE INVENTION The present invention is a continuous casting nozzle comprising a MgO-CaO-SiO ₂ -based composition containing no carbon, wherein the composition contains 5 to 87 CaO.
% By weight, 10 to 92% by weight of MgO and ₂ of SiO ₂ .
It is characterized by comprising a composition containing about 15% by weight.

This composition also contains 3% by weight or less of Al ₂
It may contain O ₃ . The refractory composition of the present invention has a composition that easily forms a liquid layer at the molten steel temperature in order to prevent the inclusion of inclusions. Further, it does not contain graphite, which has been conventionally used for improving spalling resistance in order to prevent adhesion and prevent carbon pickup.

The most notable point in the composition of the present invention is the content of SiO ₂ . MgO-C while using the nozzle
At least 2% or more of SiO ₂ is required to positively generate the aO-SiO ₂ low melting point compound. Also, S
The amount of liquid phase produced increases with an increase in the amount of iO _2, but if it exceeds 15% by weight, the melting loss becomes remarkably large, and it becomes unusable. A desirable SiO ₂ content is 3 to 12% by weight.
Further, since it is desirable to easily generate the liquid phase in order to sufficiently exert the adhesion preventing function, the SiO ₂ component is less than 0.
It is better to add fine powder of 21 mm or less, and it is preferable to use fine silica powder or amorphous ultrafine silica.

CaO and MgO also require a minimum of 5% by weight CaO and a minimum of 10% by weight MgO in order to form low melting point compounds. The ratio of CaO to MgO should be rich in CaO. Due to the grain size constitution, it is preferable that the coarse grain portion such as calcia and dolomite raw material has a large CaO content in order to maintain the fire resistance. When MgO is used alone, the amount of liquid phase produced increases,
The degree of fire resistance is reduced, resulting in excessive melting loss. The upper limit of CaO and MgO is 87% by weight of CaO, MgO
Is 92% by weight.

However, when a large amount of CaO is contained, the stability is lost in practical use due to digestion. Therefore, it is preferable that CaO is added in a particle size of 0.5 mm or more in terms of particle size constitution, and the amount is preferably in the range of 20 to 50% by weight.

As the raw material of this refractory composition, magnesia clinker, dolomite clinker, calcia clinker, silica stone, amorphous ultrafine silica, Portland cement, alumina cement and the like can be used.

Alumina cement contains a large amount of Al ₂ O ₃ , so that the fire resistance is lowered. Therefore, as described above, it is preferable to use the Al ₂ O ₃ content of 3% or less. Boltland cement is mainly composed of CaO and SiO _2.
2 Helps increase volume. The amount used is C as described above.
aO is 5 to 87% by weight, and SiO _{2 is 2 to} 15% by weight.

Metal fibers may be added for the purpose of improving spalling resistance or toughness.

The material of the fiber to be added is most preferably stainless steel from the viewpoint of corrosion resistance and structure, but not limited to this, for example, ordinary steel, carbon steel, Ni-Cr steel, Cr-M.
Non-ferrous metals such as o steel, Cr steel, Cr-V steel, Al and Al alloys may be used. The shape is most preferably φ30 to 200 μm × length 2 to 20 mm created by the chattering vibration cutting method, but the shape may be any of straight, curved, chevron, and corrugated. The addition amount of the metal fiber is preferably 5% by weight or less, and is appropriately determined according to the specific gravity of each fiber.

Further, the continuous casting nozzle of the present invention comes into contact with the molten steel such as the inner hole, the bottom and the discharge hole through which the molten steel of the nozzle formed from the C-containing refractory material such as alumina-graphite passes. The surface may be covered with the refractory composition.

As a coating method, a preformed cylindrical molded product having a length of 2 minutes or more in a horizontal direction is set in an alumina / graphite nozzle, a nozzle inner hole and A method is possible in which a core is set on the outer peripheral portion and the mixture is poured into the gap and molded. Also,
At this time, joints of 0.5 mm or more are provided between the inner hole portion, the bottom portion, and the discharge hole portion with the alumina / graphite nozzle, and the outer peripheral portion has a joint-free structure. This joint is provided in order to absorb the difference in expansion between the product of the present invention and the alumina / graphite nozzle. If the joint is less than 0.5 mm, the expansion of the product of the present invention causes cracks in the alumina / graphite nozzle. Considering corrosion resistance, the thickness of the coating is preferably 5 mm or more.

The composition of the present invention has low fire resistance and poor spalling resistance as compared with conventional alumina-graphite nozzles. Therefore, in order to effectively use the product of the present invention, it can be used as a coating material for nozzles of conventional refractory materials containing carbon such as alumina / graphite, zirconia / graphite, magnesia / graphite.

Particularly, the main body is excellent in spalling resistance, corrosion resistance, strength, etc., of alumina / graphite, zirconia /
In the case of a graphite material, even if it contains carbon, if it is combined with the present coated refractory composition, a composite molded body thereof can be easily produced, and the effect can be exhibited without losing both properties.

[0026]

The MgO-CaO-SiO ₂ system forms a lower melting point compound than the conventional Al ₂ O ₃ -CaO refractory composition in the SiO ₂ rich region, and has a wide liquid phase generation region near 1500 to 1550 ° C. . Further, the melting point is further lowered by the reaction with alumina.

[0027]

EXAMPLES Each attached drawing shows the structure of a nozzle to which the refractory composition of the present invention is applied, and shows an example in which the surface in contact with molten steel is coated with the refractory composition of the present invention.

FIG. 1 shows a long nozzle arranged below the pan bottom nozzle A, in which the main body 1 is made of alumina / graphite refractory material and the zirconia / graphite refractory material 2 is attached to the slag line. A refractory layer 6 containing no carbon is provided on the inner hole surface 3 and the lower outer periphery 4 thereof through a joint material 5.

FIG. 2 shows an example of a submerged nozzle arranged under the tundish lower nozzle B, in which the inner hole surface 3 of the main body 1, the molten steel discharge hole 7 and the lower outer circumference 4 are carbonized through the joint material 5. An example in which the refractory layer 6 not containing is provided.

Further, FIG. 3 shows an example in which it is applied to an integral type immersion nozzle, and the inner bore surface 3 including the opening bosh portion 8 of the main body 1 is shown.
An example is shown in which a refractory layer 6 containing no carbon is provided on the molten steel discharge hole 7 and the lower outer periphery 4 through the joint material 5.

In the examples shown in the above figures, each nozzle may be formed from the carbon-free refractory composition of the present invention.

Table 1 shows the composition and chemical composition of the carbon-free refractory layer 6 shown in each of the above figures, and the compositional composition of the constituent raw materials by weight%. The refractory composition constituting the main body as a comparative example. A characteristic comparison with is shown.

[Table 1] ★

Using the compositions shown in the table, the nozzles shown in the above figures were manufactured and subjected to an actual furnace test as a measure for preventing nozzle clogging.

The results of comparison of the aluminum-killed steel cast with the conventional alumina-graphite nozzle are shown in Table 1 for inclusion deposit thickness. The inclusion of inclusions in the nozzle using the composition of the present invention was scarcely present, and the number of non-metallic inclusions, surface defects and internal defects of the slab were reduced, showing good results. Further, according to the present invention, nozzle clogging is less likely to occur, and stable operation can be performed.

Further, as a result of being used for casting ultra low carbon steel,
Compared with the case of using the conventional alumina-graphite nozzle, the long nozzle has a carbon pick-up preventing effect of 3.5 ppm, and the immersion nozzle has a carbon pick-up preventing effect of 1.5 ppm (Fig. 4).

FIG. 4 shows the C contents of the ladle after completion of secondary refining, the sample obtained from the tundish during casting and the product, and ΔC is between the ladle and the tundish, and the tundish. -Indicates the amount of carbon pickup between products.

[0037]

The use of the refractory composition of the present invention has the following effects.

(1) Since it forms a low melting point compound having a wide range of liquid phase forming region with a low melting point while having a refractory degree that can withstand the casting of molten steel, it is more difficult than a conventional Al ₂ O ₃ —CaO refractory composition. It has excellent adhesion.

(2) Even in the casting of ultra low carbon steel, carbon pickup to molten steel can be effectively prevented.

(3) In the case of a combination of a main body made of a refractory containing carbon and a coating layer of a refractory composition not containing carbon, in addition to the effects of (1) and (2), the life of the continuous casting nozzle is extended. Can be measured.

[Brief description of drawings]

FIG. 1 shows an embodiment applied to a long nozzle.

FIG. 2 shows an embodiment applied to an immersion nozzle.

FIG. 3 shows an embodiment of an integrated immersion nozzle.

FIG. 4 shows a C pickup in each step.

[Explanation of symbols]

A Pan bottom nozzle B Tundish bottom nozzle 1 Nozzle body 2 Slag line refractory material 3 Nozzle inner hole surface 4 Nozzle lower outer peripheral surface 5 Joint material 6 Carbon-free refractory layer 7 Molten steel discharge hole 8 Opening bosh

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C04B 35/043 (72) Inventor Yukihisa Matsuo 1-1 Higashihama-cho, Hachimansai-ku, Kitakyushu, Fukuoka Prefecture Kurosaki Ceramic Industry (72) Inventor Ryoji Nishihara 1-1 Hibahata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Inside Nippon Steel Co., Ltd. Yawata Works (72) Inventor Tomomi Inada 1-Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka No. 1 New Nippon Steel Co., Ltd., Yawata Works (72) Inventor Hiroyuki Ishimatsu 1-1 No. 1 Tobatacho, Tobata-ku, Kitakyushu, Kitakyushu, Fukuoka Prefecture (72) Inventor, Yajita Matsui, Yasujiro Matsui Fukuoka Prefecture 1-1 Hibata-cho, Tobata-ku, Kitakyushu City Inside the Yawata Works, Nippon Steel Corporation

Claims (4)

[Claims] 1. A carbon-free MgO-CaO-S.
A continuous casting nozzle comprising an iO ₂ -based composition,
The composition contains 5 to 87 wt% CaO and 10 to MgO.
A continuous casting nozzle comprising a composition containing 92% by weight of SiO ₂ and ₂ to 15% by weight of SiO ₂ . 2. The composition of claim 1, wherein the MgO—CaO—SiO ₂ -based composition containing no carbon is Al ₂ O.
A continuous casting nozzle comprising a composition containing ₃ and 3% by weight or less. 3. A nozzle for continuous casting, wherein a refractory composition layer containing no carbon is provided at a portion of a main body made of refractory containing carbon, which is in contact with molten steel, wherein the refractory composition layer is M.
It consists gO-CaO-SiO ₂ based composition, and from 5 to 87 wt% of CaO, and 10 to 92 wt% of MgO, Si
A nozzle for continuous casting, comprising a composition containing ₂ to 15% by weight of O ₂ . 4. The composition of claim 3, wherein the MgO—CaO—SiO ₂ -based composition containing no carbon is Al ₂ O.
A continuous casting nozzle comprising a composition containing ₃ and 3% by weight or less.