JP2937450B2 - Immersion nozzle for continuous casting - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a continuous casting immersion nozzle which can be used for a long time in casting molten steel from a tundish into a mold in continuous casting of steel. is there.

[Conventional technology]

Conventionally, as a submerged nozzle refractory for continuous casting, an alumina-graphite-based refractory added with silica, which has a low expansion property to withstand continuous casting of steel, is generally used.

However, silica in refractories reacts with strong reducing elements such as Mn, Al, and Ti in molten steel and melts out into molten steel,
A problem arises in the corrosion resistance to molten steel.

For this reason, in an alumina graphite-based steel casting molten nozzle, the main body contains 10 to 35 wt% of silica, and the molten steel immersion part and / or the inner peripheral hole of the nozzle do not contain silica or contain less silica than the main body. The proposed molten steel casting nozzle has been proposed (Japanese Patent Publication No. 1-40790) to ensure corrosion resistance to molten steel.

In addition, as a low expansion material, clay other than silica, an oxide containing SiO ₂ such as zircon is added, and while ensuring spalling resistance, SiO ₂ and Mn, Al, Ta in molten steel are added.
A method for suppressing the reaction with benzene has also been reported (Japanese Patent Application Laid-Open No.
572, JP-A-61-83673).

[Problems to be solved by the invention]

The method of reducing the silica content of the molten steel immersion section,
It is effective for improving the corrosion resistance because the reaction with molten steel is suppressed. However, since the thermal expansion coefficient of the portion where silica is reduced becomes large, there is a disadvantage that a thermal expansion difference occurs between the nozzle body and the immersion portion, and the spalling resistance is reduced.

In the case of an oxide containing SiO ₂ ,
The SiO ₂ component reacts with C coexisting in the nozzle refractory and volatilizes and disappears, thereby forming pores in the refractory structure and lowering the strength, and also promotes infiltration of molten steel into the refractory and lowers corrosion resistance. The problem arises.

In view of the above problems, the present invention is to provide a continuous casting immersion nozzle that eliminates the deterioration of the corrosion resistance and spalling resistance of the immersion nozzle and does not cause such defects even when used for a long time. It is the purpose.

[Means for solving the problem]

The present invention provides an aluminum-graphite molten steel casting nozzle comprising aluminum titanate in an amount of 5 to 90% by weight and a silica content of 5% by weight or less, which is excellent in corrosion resistance and spalling resistance. It relates to an immersion nozzle for continuous casting.

(Operation)

The inventors have reduced the silica content to a level that does not cause a problem in ensuring the corrosion resistance of the immersion nozzle, and then compensated for the decrease in spalling resistance based on the reduced silica content, or equivalent to silica, or The research and development of the immersion nozzle which is excellent in corrosion resistance and spalling resistance by adding the material having the above low expansion coefficient has been continued. As a result, silica
The corrosion resistance and spalling resistance were significantly improved by reducing the content to 5 wt% or less and further adding 5 wt% or more of aluminum titanate (Al ₂ O ₃ TiO ₂ ) as a low expansion material.

Silica having low expansion properties plays an important role in increasing the spalling resistance of the immersion nozzle. However, when the molten steel contains elements with strong reducibility such as Mn, Al, and Ti, the silica reacts with these elements and melts out into the molten steel. Silica is also reduced by carbon coexisting in the nozzle, volatilizes and disappears, and generates pores in the refractory. Therefore, the nozzle containing silica has a drawback that it has poor corrosion resistance to molten steel. For this reason, it is preferable that no silica is contained as a constituent component of the refractory, but if necessary, it may be used in an amount of 5 wt% or less. This is because when the silica content exceeds 5% by weight, the corrosion resistance rapidly decreases.

The coefficient of thermal expansion of aluminum titanate is -0.5 × 10 ^-6
It is in the range of 2.02.0 × 10 ⁻⁶ 1 / ° C., and apparently can have a negative coefficient of thermal expansion. Therefore, spalling resistance can be significantly improved by adding aluminum titanate having low expansion properties to the refractory. Furthermore, the melting point of aluminum titanate is as high as 1860 ° C, and it has sufficient heat resistance even at the casting temperature of molten steel (about 1550 ° C). Further, since Al ₂ O ₃ and TiO ₂ are very stable oxides alone, aluminum titanate to which these oxides can be combined can be more stably present. Therefore, it does not react with elements having strong reducibility such as Mn, Al, and Ti in the molten steel and does not melt into the molten steel. Here, the content of aluminum titanate is 5 to 90 wt%. 5wt%
If it is less than 90% by weight, it is not possible to compensate for the decrease in spalling resistance due to the decrease in silica content. to degrade.

Since graphite has extremely high thermal conductivity and is very hard to wet with molten steel, in the present invention, graphite is added to the extent that corrosion resistance is not reduced, and molten steel and powder are prevented from entering the pores of the immersion nozzle. And improve the spalling resistance. As a raw material for use of graphite, natural phosphorous graphite is preferable. However, as long as it is generally used for refractories, it can be used unless the ash content is excessive. The range of graphite is preferably about 5 wt% to 50 wt%. 5wt%
If it is less than 50%, spalling resistance is inferior. If it exceeds 50% by weight, corrosion resistance to molten steel and molten powder is reduced due to oxidation of graphite and elution into molten steel. In addition, nozzle clogging may occur due to high thermal conductivity.

Alumina has a role of imparting corrosion resistance, purity 90 wt%
The above electrofused or sintered product is used. The preferred compounding ratio is
35wt% ~ 90wt%, less than 35wt%, the corrosion resistance is insufficient,
If it exceeds 90 wt%, the spalling resistance tends to decrease.

Although the basic components of the immersion nozzle are as described above, other materials that are already known as additives to the material of the nozzle may be contained as long as the effects of the present invention are not impaired. As the material, for example, silicon carbide, zirconia,
Gyricon, various metal powders, and the like.

In addition, the present inventor has investigated the cause of the occurrence of blistering defects ranging from 1 to 4 mm in width and several mm in length appearing on a steel sheet after hot rolling and cold rolling, and was blown to prevent clogging of the immersion nozzle. Was found to be caused by coarsening of the Ar bubbles. Furthermore, they found that the coarsening of Ar bubbles was due to the selective erosion of silica in the immersion nozzle by Al, Ti, and Mn in the molten steel, and the pore diameter in the refractory expanded. Therefore, if the present invention is applied to an alumina-graphite gas blowing type immersion nozzle, the pore diameter can be prevented from expanding, and the blowing gas can be stably and finely blown. It is an effective means.

Graphite-alumina nozzles having a silica content of 5 wt% or less and containing aluminum titanate in an amount of 5 to 90 wt%, as described above, are superior in both corrosion resistance and spalling resistance as compared with conventional nozzles. The continuous casting operation was enabled and the slab quality was greatly improved.

〔Example〕

Hereinafter, the present invention will be described with reference to Examples and Comparative Examples.

12 wt% of a phenolic resin was added as a resin binder to the raw material blends shown in Table 1 and kneaded, and the mixture was formed into a nozzle shape at a pressure of 1.0 t / cm ² using an isostatic press.

Further, the molded body was reduced and fired at a temperature of 1200 ° C. to produce a gas injection type immersion nozzle for continuous casting (inverted Y-type nozzle having an inner diameter of 90 mmφ, a discharge hole diameter of 70 mmφ, and a discharge hole angle of 35 °). Using the immersion nozzle obtained in this way, Ti
Ultra low carbon steel containing 0.08 wt% and having a carbon concentration of 30 ppm was cast for 400 minutes. The spalling resistance was evaluated using the time at which cracks occurred in the immersion nozzle as an index. The value obtained by dividing the amount of refractory erosion in the nozzle by the casting time was defined as the erosion rate, and the corrosion resistance was also evaluated.

 Table 2 shows the quality evaluation results of Examples and Comparative Examples.

The nozzles of Examples 1, 2 and 3 could be cast for 400 minutes without cracking. The inner diameter of the nozzle is 90 mm to 94.0 mm for the nozzle of Example 1 (melting speed 0.005 mm / min).
Then, the nozzle of Example 2 was used to measure 90 mm to 93.2 mm (melting speed 0.00
4 mm / min), the nozzle of Example 3 expanded from 90 mm to 92.4 mm (melting speed 0.003 mm / min), but no remarkable erosion was observed. Furthermore, no swelling defect occurred in the slabs cast using the nozzles of Examples 1, 2 and 3 after cold rolling.

The nozzle of Comparative Example 1 conventionally used was able to be cast for 400 minutes, but the nozzle inner diameter was 90 mm to 110 mm (the erosion speed was 0.0 mm).
25mm / min), and the amount of erosion of the nozzle was large. In addition, swelling defects occurred in the slab after cold rolling.

In the nozzle of Comparative Example 2 in which the content of aluminum titanate was less than 5 wt%, a crack was generated 200 minutes after the start of casting, and the casting was stopped. At this time, the inner diameter of the immersion nozzle is 90 mm to 91 mm
(Corrosion resistance was good only by expanding to (melting speed 0.0025 mm / min). Therefore, after the cold rolling, no swelling defect occurred in the cast slab.

The content of aluminum titanate was within the range of the present invention, and the nozzle of Comparative Example 3 containing more than 5 wt% of silica could be cast for 400 minutes, but the nozzle inner diameter was 90 mm to 104 mm.
mm (erosion rate 0.0175 mm / min), corrosion resistance deteriorated, swelling defects occurred in the slab after cold rolling, and the content of aluminum titanate exceeded 90 wt%. Nozzle was cracked 175 minutes after the start of casting, and the casting was stopped. At this time, the inner diameter of the immersion nozzle is 90 mm
The corrosion resistance was good only by expanding to 90.7 mm (melting speed 0.02 mm / min). Therefore, no swelling defect occurred in the slab after cold rolling.

As described above, the immersion nozzle manufactured according to the present invention is not only excellent in corrosion resistance and spalling resistance, but also can sufficiently secure the quality of the slab.

[Effects of the Invention] As described above, according to the continuous casting immersion nozzle of the present invention, the corrosion resistance to molten steel and mold powder is good, and further, since it has an effect excellent in spalling resistance, It can be used stably for a long time, and greatly improves operability. In addition, since it has excellent heat resistance, stable gas injection is possible, and blistering defects can be prevented. Therefore, the quality of the steel sheet manufactured by the continuous casting method is very stable, and the yield is remarkably improved.

Continuation of the front page (56) References JP-A-56-14061 (JP, A) JP-A-63-170260 (JP, A) JP-A-63-248767 (JP, A) JP-A-54-77608 (JP) JP-A-57-118068 (JP, A) JP-A-3-243257 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22D 11/10 330 C22D 41/54 C04B 35/10

Claims (1)

(57) [Claims] 1. An aluminum-graphite molten steel casting nozzle comprising aluminum titanate in an amount of 5 to 90% by weight and a silica content of 5% by weight or less, which is excellent in corrosion resistance and spalling resistance. Immersion nozzle for continuous casting.