JPH05154628A - Nozzle inner hole body for continuous casting - Google Patents

Abstract

PURPOSE:To reduce non-metallic inclusions, surface defect and internal defect in a steel by using a nozzle inner hole body containing the specific composition of alumina clinker as the specific component and having refractory composition containing the specific compositions of alumina, carbon and silica and the specific grain size constitution. CONSTITUTION:The nozzle inner hole body for continuous casting is made of the alumina clinker of >=99wt.% alumina content as the substantial component and the refractory composition of >=70wt.% the alumina content, <1wt.% the carbon content, <1wt.% the silica content and the grain size constitution having 20-70% of <=0.21mm grain size. The nozzle is formed with e.g. alumina- graphite quality refractory 1, inner hole body 2 and alumina mortar layer 3. By this method, carbon pickup in the extremely low carbon steel casting can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal hole body which is inserted into a hole portion of a continuous casting nozzle which is used by being attached to a ladle, a tundish or the like in the continuous casting of steel.

[0002]

2. Description of the Related Art In continuous casting, molten steel is transferred from a ladle to a tundish or from a tundish to a mold through a nozzle such as a long nozzle, a tundish nozzle or a dipping nozzle.

An alumina / graphite refractory having excellent corrosion resistance and spalling resistance is used for this nozzle.

In recent years, there has been an increasing demand for a high degree of purification with the demand for improving the workability of steels such as steel sheets for automobiles, and a high degree of cleanliness without inclusions for tins for DI cans, shadow mask materials, etc. It is desired to prevent carbon pickup in the continuous casting process and to manufacture steel with less surface defects and internal defects.

As a measure for preventing this carbon pickup, technical developments such as reduction of carbon content of tundish coating material and reduction of carbon content of continuous casting flux have been carried out.

[0006] As measures against inclusions, efforts are being made to reduce inclusions in steel by degassing molten steel, absorbing nonmetallic inclusions by a tundish weir, or floating.

However, in the current alumina / graphite nozzle, carbon has a drawback that it is difficult to obtain stable workability of the product by the carbon pickup due to the outflow of carbon from the damaged portion of the operating surface during casting. Also, in aluminum killed steel such as tin materials for various cans, nozzle clogging of the nozzle for continuous casting often occurs due to precipitation of alumina in the steel, the number of continuous casting is small, production efficiency decreases, and molten steel flow due to partial clogging Turbulence occurs, the nozzle is worn, and the inclusion of refractory increases.

Ar gas is blown in to prevent the nozzle from being clogged by alumina, but the surface defects and inclusions of steel are caused by the inclusion of continuous casting flux due to the turbulence of the molten steel flow, the inclusion of Ar gas, and the like. Are trapped, and there are various problems in producing a homogeneous and clean steel.

It is considered that the clogging of the nozzle due to this alumina occurs as follows.

(1) Alumina is produced by the oxidation of aluminum in steel by air and the secondary oxidation by oxygen generated by the reaction between silica and carbon in the refractory.

(2) Alumina clusters are formed by the diffusion and aggregation of this alumina.

(3) Due to the disappearance of carbon on the operating surface of the nozzle, the surface becomes uneven.

(4) 50 to 50 near the working surface of this nozzle
There is a laminar flow region with a flow velocity close to 0 at a thickness of 100 μm, and alumina clusters adhere to the inner wall surface in this laminar flow region due to the difference in specific gravity with the molten steel or the physical adhesive force.

(5) Mn and S in molten steel between the clusters
A liquid phase of oxides such as i, Ca, and Mg is attached, a strong alumina cluster layer is formed, and the alumina cluster layer is gradually thickened to cause nozzle clogging.

In order to prevent such a nozzle clogging of the continuous casting nozzle, Japanese Patent Laid-Open No. 165548/56,
JP-A-57-38366 and JP-A-57-563
No. 77 discloses a nozzle for continuous casting using lime / carbonaceous brick.

The lime clinker of the lime / carbonaceous continuous casting nozzle reacts with the alumina precipitated from the molten steel to become a low melting point substance such as CaO.Al ₂ O ₃ , 3CaO.Al ₂ O ₃ and the inner wall of the nozzle. It is said that it has an effect of preventing nozzle clogging because it flows without staying in the nozzle. Furthermore, S is used to prevent digestion of the lime clinker that forms this lime.
By adding metal powders such as i, Al, Fe and Ni or stabilizers such as BN and B ₄ C, it is possible to prevent digestion to some extent. However, even if any stabilizer is used, the digestion of lime clinker cannot be suppressed, and there are various restrictions in terms of use and control as compared with the alumina / graphite nozzle.

That is, it is very difficult to sufficiently check the occurrence of cracks in the nozzle due to the digestion of lime clinker at the site of use, and the risk of nozzle breakage during use is always present. Furthermore, although carbon enhances thermal shock resistance in lime / graphite nozzles, on the other hand, it has a high thermal conductivity, facilitates cooling of molten steel, and serves as an oxygen supply source for alumina generation, causing the generation of inclusions. There is.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inner hole body of an alumina nozzle capable of reducing carbon pickup of molten steel and preventing generation and adhesion of alumina in steel.

[0019]

The nozzle inner bore for continuous casting according to the present invention comprises an alumina clinker having an alumina content of 99% by weight or more as a main component and an alumina content of 70% by weight.
As described above, the refractory composition has a carbon content of less than 1% by weight and a silica content of less than 1% by weight, and is 0.21 mm.
The object was achieved by having a particle size composition in which the following particle sizes account for 20-70%.

The alumina raw material used for the inner pores of the present invention is
An electromelted or sintered clinker can be used, and in terms of composition, the Al ₂ O ₃ content is 99% by weight or more.

Metal fibers may be added to the refractory composition to strengthen the matrix. The most preferred material is stainless steel from the viewpoint of corrosion resistance and structure,
Not limited to this, for example, iron, carbon steel or Ni-Cr steel,
Non-ferrous metals such as Cr-Mo steel, Cr steel, Cr-V steel, Al and Al alloys may be used. As the metal fiber, the shape is φ30 to 100 created by the chatter vibration cutting method.
The most preferable is μm × 2 to 20 mm, but any of straight, curved, mountain-shaped, and parallel-shaped shapes may be used. The amount of metal fibers added is in the range of 5% by weight or less, and is appropriately determined according to the specific gravity of each fiber. Although the effect is recognized even with a very small proportion, the metal fiber is also a low melting point substance, and if added excessively, the corrosion resistance is deteriorated due to an increase in added water, and the effect of the present invention cannot be obtained. Further, the preferable addition amount is 0.1 to 3% by weight.

In forming the continuous casting nozzle inner hole body of the present invention, the alumina / graphite long nozzle and the dipping nozzle are internally filled and simultaneously formed, or by pouring into a metal frame or the like, or by pressing. Any method may be used in which the inner hole is formed and then the alumina / graphite nozzle is inserted and filled.

In the molding, a hydraulic binder may be used, for example, alumina cement may be used. Alumina cement has CaO content of 0.5-5% by weight
It is necessary to develop sufficient strength in the range of, and high-alumina cement and super-high-alumina cement having a low CaO content and good strength development are suitable. The use ratio of the alumina raw material of the fine powder and the alumina cement is the amount of CaO because the CaO in the alumina cement and the fine alumina powder react as the production minerals of the material and CaO · 6Al ₂ O ₃ is formed to give the expandability. On the other hand, 1: 6 wt% or more of Al ₂ O ₃ is required.

[0024]

The present invention has been studied from the five factors of reducing the amount of silica in the refractory, smoothing the operating surface roughness, lowering air permeability, that is, densifying, improving the heat insulating effect, and suppressing the outflow of carbon. Alumina that reduces carbon pickup in molten steel and prevents the formation and adhesion of alumina in the steel.
An inner hole of a graphite nozzle was obtained.

The alumina content of 70% by weight or more means that Fe in the high-oxygen steel or weakly deoxidized steel is cast in the steel.
This is because the O and MnO concentrations are high, and if the alumina content is less than 70% by weight, the melting loss is large and the function of the inner pore body cannot be exhibited.

Also, general steels other than special steels such as high-oxygen steels and weakly deoxidized steels have the same tendency although the levels of erosion rates are different. From the viewpoint of purification, the alumina content is 70% by weight
The above is necessary.

When the particle size composition of 0.21 mm or less is less than 20% by weight, the composition is out of the close-packed composition, so that the effect of the present invention can be obtained from the relations of structure densification, increase in air permeability and surface roughness. Is not expected. On the other hand, if it exceeds 70% by weight, the amount of fine powder becomes excessive, which causes a problem of volume stability.

[0028]

1 to 8 show examples of nozzles to which the present invention is applied, FIGS. 1 to 4 show examples of immersion nozzles, and FIG.
8 shows an example of a long nozzle. In these figures, 1 is an alumina-graphite refractory material, 2 is the arrangement of the nozzle inner hole body according to the present invention, and the thickness of the alumina-graphite refractory material 1 is made larger than the thickness of the inner hole body 2. Is forming. 4, 6 and 8 show an example in which an alumina mortar layer 3 having an expansion absorbing function is provided on the back surface of the inner hole body.

Example 1 A refractory aggregate having 99% by weight or more of alumina, 0.21
45% by weight of particles with a diameter of mm or more, 40% by weight of particles with a diameter of less than 0.21 mm, super high alumina cement 15
A weight percent refractory material was obtained. The composition of this is shown in Table 1. To this refractory, 2% of a metal fiber made of SUS having a size of 90 μm × 6 mm was externally added. This characteristic is also shown in Table 1.
Shown in. For comparison, the comparative composition of Table 1 and a conventional alumina-graphite refractory were prepared.

[0030]

[Table 1] From these refractories, a continuous casting nozzle inner hole was lined in the long nozzle and the immersion nozzle inner hole to obtain the nozzle shown in FIGS. 4 and 8. As a measure to prevent carbon pickup in continuous casting of ultra-low carbon steel, it was subjected to an actual machine test.

As a result of the test, as compared with the case where the conventional alumina graphite material nozzle is used, the effect of reducing the carbon pickup is seen as shown in FIG. In addition, no cracks were formed in the inner nozzles of the long nozzles and the immersion nozzles, and the base material, and the melting loss of the inner nozzles was much smaller than that of alumina graphite as shown in FIG. 10. It could be reused.

Example 2 A refractory aggregate having 99% by weight or more of alumina shown in Table 1 and 50% by weight of particles having a diameter of 0.21 mm or more,
Particles having a diameter of less than 0.21 mm had a particle size constitution of 50% by weight, and a nozzle shown in FIG. 3 was prepared from a refractory material having the characteristics shown in the table and subjected to an actual machine test.

When aluminum-killed steel was cast and compared with a conventional alumina-graphite nozzle, FIGS.
As shown in Table 1, the product of the present invention showed almost no inclusions, and the number of non-metallic inclusions in the slab and the number of surface defects and internal defects were small, showing good results.

Further, due to the heat retaining effect, no metal adhesion was observed on the operating surface of the inner hole body of the present invention.

[0035]

EFFECTS OF THE INVENTION By using the continuous casting nozzle inner hole body of the present invention, carbon pickup in extremely low carbon steel casting is reduced, and nozzle clogging due to formation of the alumina cluster layer of the continuous casting nozzle is prevented. However, it is possible to reduce non-metallic inclusions, surface defects and internal defects in the steel.

Therefore, it contributes sufficiently to high purification and cleaning of steel, and can greatly improve the quality of steel.

[Brief description of drawings]

FIG. 1 shows an immersion nozzle as an example of an application nozzle of the present invention.

FIG. 2 shows another example of the immersion nozzle.

FIG. 3 shows another example of the immersion nozzle.

FIG. 4 shows another example of the immersion nozzle.

FIG. 5 shows a long nozzle as an example of an applicable nozzle of the present invention.

FIG. 6 shows another example of a long nozzle.

FIG. 7 shows another example of a long nozzle.

FIG. 8 shows another example of a long nozzle.

FIG. 9 shows a comparison of the states of the pickup of C as the effects of the embodiment of the present invention and the comparative example.

FIG. 10 shows a comparison of the amount of erosion loss in the inner hole portion.

FIG. 11 shows a comparison of the thickness of inclusions.

FIG. 12 shows a comparison of product failure occurrence rates.

[Explanation of symbols]

 1 Alumina-graphite refractory 2 Inner pore 3 Alumina mortar layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kei Nishi Nishi 1-1, Higashihama-cho, Hachiman-nishi-ku, Kitakyushu, Fukuoka Prefecture Kurosaki Ceramics Co., Ltd. Inside Nippon Steel Co., Ltd. Yawata Works (72) Inventor Ryoji Nishihara No. 1 Tobahata-cho, Tobata-ku, Kitakyushu City, Kitakyushu, Fukuoka Prefecture (72) Inventor Shinichi Fukunaga Kitakyushu, Fukuoka Prefecture No. 1-1 Toibata-cho, Tobata-ku, Shizuoka Inside the Yawata Works, Nippon Steel Corporation

Claims (1)

[Claims] 1. A refractory composition containing, as a main component, an alumina clinker having an alumina content of 99% by weight or more, an alumina content of 70% by weight or more, a carbon content of less than 1% by weight, and a silica content of less than 1% by weight. And has 0.21 m
A nozzle inner hole body for continuous casting having a particle size constitution in which a particle size of m or less accounts for 20 to 70%.