JPS62148076A - Nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To decrease the sticking of inclusions to an inside wall by incorporating unstabilized zirconia having specific grain sizes and graphite respectively at prescribed weight % into the titled nozzle and constituting the balance of stabilized zirconia having a prescribed grain size. CONSTITUTION:The nozzle is constituted by incorporating 35-75% unstabilized zirconia adjusted to <=100mu grain size and 5-15% graphite components therein and consisting of the balance stabilized zirconia adjusted to <=100mu grain size. The grain sizes of both the unstabilized zirconia and the stabilized zirconia are adjusted to <=100mu in order to prevent the sticking of the inclusions to the inside wall of the nozzle and to improve spalling resistance while maintaining the corrosion resistance of the nozzle to adequately distribute the graphite components. Since the ratio of the unstabilized and stabilized zirconia is adequate, the sticking of the inclusions is prevented. The sticking of the inclusions to the inside wall of the nozzle as a whole is thus decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a continuous casting nozzle for the purpose of reducing the slippage of inclusions that occur during steel casting.

(Prior Art) Conventionally, in casting nozzles, for example, immersion nozzles, when casting aluminum killed liquid to which aluminum is added as a deoxidizing agent, alumina adheres and grows on the alumina-graphite inner wall of the nozzle, causing nozzle blockage. This is causing problems when used multiple times.

(Problems to be Solved by the Invention) Therefore, as a preventive measure, an inert gas is blown into the nozzle inner tube to physically remove the deposits.

However, since a large amount of inert gas is used and the structure is complicated, the cost is high, and the effectiveness varies widely, and it is also possible to remove deposits that have grown to a certain extent, resulting in defective slabs. It can be seen.

On the other hand, as a countermeasure from a material standpoint, non-oxide raw materials (Sin
, Si3 N, , BN, ZrB2. Since the reactivity of aluminum oxide (such as SIAON) with aluminum oxide is low, a nozzle consisting of a non-oxide raw material added to alumina-graphite or itself has been proposed.

However, when it is added to alumina-graphite, unless it is added in a large amount, the anti-adhesion effect will not be realized and the corrosion resistance will deteriorate, so it is not suitable for automobiles.

Also, when creating a nozzle using only non-oxide materials,
Although this method is expected to be effective, it is not suitable for practical use due to the cost of raw materials and manufacturing.

(Means for Solving the Intermediate Point) The inventors of the present application investigated alumina adhesion that occurs in conventional alumina-graphite immersion nozzles, and obtained the following findings.

When observing the boundary between the nozzle inner wall and the alumina deposits of a conventional alumina-graphite nozzle that caused nozzle blockage, it was found that the deposits tended to enter four parts of the inner wall. These four parts were caused by the outflow of aggregate from the alumina-graphite nozzle.
The deposits react with and bond with the fine alumina powder of the matrix. Several factors can be considered for this reaction, including sintering through slag, sublimation of silica (S1O), which is usually added to alumina-graphite.
The main reaction is the oxidation reaction of aluminum in steel.

Furthermore, the alumina particles present in the steel and the adhesion of crystallized alumina particles caused by the temperature drop near the inner wall of the nozzle are considered to be secondary products of the above reaction.

Therefore, in order to suppress alumina adhesion, it is effective to reduce the unevenness of the inner wall surface, which is a factor in the initial adhesion. It is also desirable that the material itself has low reactivity with alumina.

Based on the above-mentioned findings, the inventors of the present application conducted three tests on fine particles of common anti-fabric raw materials such as silconium, magnesia, and calcia, and non-oxide raw materials such as silicon carbide, silicon nitride, and boron nitride.
It is clear from experience that if a continuous casting nozzle, especially a submerged nozzle, is made using only the above-mentioned raw materials, the spalling resistance required for a submerged nozzle cannot be met. Moreover, in the case of basic raw materials such as magnesia and calcia, there are problems with water usage in the atmosphere and high coefficient of thermal expansion, and in order to put them into practical use, treatment to prevent water usage and the addition of large amounts of graphite are not only difficult, but also difficult. , no adhesion prevention effect can be expected.

Further, non-oxide raw materials have sufficient spalling resistance, but silicon carbide and silicon nitride have insufficient corrosion resistance, and other materials are extremely expensive. Therefore, zirconia-graphite, which is currently commonly used as a powder line material for immersion nozzles, is considered to be optimal. Below, we will discuss the results of examining the zirconia particle size, the amount of graphite added, and the blending ratio of stabilized zirconia and unstabilized zirconia.

/) Examination of zirconia particle size As a zirconia raw material soo~/joμ, B; 0~1
A total of 6 types of stabilized zirconia and unstabilized zirconia with particle sizes of 00μ and 100μ or less were mixed in the following composition, molded in an isostatic press, fired in a coke spray, and tested. I got a body.

Table 1 Grain size study table/The test specimen was cut into a size of 30 x 30 x 230 Ctnm), used as a test piece, and immersed in a high frequency induction furnace in which steel was melted.
No adhesion was observed in composition 3 and B, which were composed of zirconia with a diameter of less than μ, whereas adhesion was observed in the other compositions.

Therefore, it seems that the adhesion of inclusions can be prevented only when the particle size of the zirconia used is 10 μm or less. , 2) Examination of the amount of added graphite/) Similarly to (), a test specimen with the following composition was preheated and immersed in molten steel to determine the spalling resistance.

Table 2 Examination of the amount of graphite If the amount of graphite is less than 5%, inclusions are observed, although slight, and the spalling resistance deteriorates.

On the other hand, when /j% was exceeded, although no inclusions were observed, the amount of erosion was large, and the amount remaining after the immersion test was significantly inferior to the others.

Therefore, it seems appropriate to add graphite in an amount of 5 to 75%.

3) Examination of the blending ratio of stabilized zirconia and unstabilized zirconia - The same test as in ) was conducted using the following composition, and the appropriate blending ratio of stable zirconia and unstabilized zirconia was investigated.

Table 3 Examination of the blending ratio of zirconia When the ratio of unstabilized zirconia exceeds 7S%, the abnormal thermal expansion that occurs during heating is not sufficiently alleviated, and the spalling resistance is significantly deteriorated.

Furthermore, if the ratio of unstabilized zirconia is less than 35% and the ratio of stabilized zirconia exceeds 50%, inclusions will adhere due to the influence of calcia dissolved in the stabilized zirconia.

Therefore, it seems appropriate that the blending ratio of unstabilized zirconia is 35 to 75% depending on the amount of graphite added.

Based on the results of the studies in /), , 2), and 3) above, 10011m was selected as a composition that prevents the adhesion of inclusions and has spalling resistance and corrosion resistance that can be applied to continuous casting nozzles.
The following composition is determined: 35 to 75 parts by weight of unstabilized zirconia, 5 to 75 parts by weight of graphite, and the remainder being stabilized zirconia of 100 μm or less.

If the particle size exceeds 700 μm, the unevenness on the surface of the material will be large enough to trap inclusions, and the effect of preventing stickiness will be drastically reduced.

Furthermore, when the blending ratio of unstabilized zirconia is less than 35 parts by weight, the blending ratio of stabilized zirconia exceeds 50 parts by weight, so that the amount of calcia and magnesia added as stabilizers is sufficient to react with the intervening US. As a result, the adhesion prevention effect is reduced.

On the other hand, if the blending ratio of unstabilized zirconia exceeds 75 parts by weight, the spalling resistance deteriorates due to the thermal expansion characteristics of zirconia, making practical use impossible.

Furthermore, if the amount of graphite added is less than 5 parts by weight, not only will the spalling resistance deteriorate, but graphite itself will not have the adhesion prevention effect, so it will tend to stick. Conversely, if it exceeds 75 parts by weight, the corrosion resistance will be lower than that of the conventional one. It is lower than alumina-graphite and is not suitable.

(Effect of the invention) Next, the effects of this invention will be described with reference to Examples.

Example/.

Unstabilized ZILL 33750 with particle size adjusted to 100μ or less
33 parts by weight of stable zirconia and 3 parts by weight of spiral graphite were mixed together with 7 parts by weight of phenol resin, and the mixture was fired in a molded coke pleat using a rubber press to form a submerged nozzle shape.

When the obtained immersion nozzle was used in Kosha's bloom continuous casting machine, the conventional alumina-graphite immersion nozzle became unable to cast after the 3rd charge, but the product of the present invention could not be cast completely after the 3rd charge. However, no inclusions were observed to adhere to the inner wall.

Example 2 Unstabilized zirconia 7j adjusted to particle size of 100μ or less
7 parts by weight of phenol resin were mixed with parts by weight of unstabilized zirconia IS, 70 parts by weight of scaly graphite, and a tundish nozzle was formed using a Frixi blade press, followed by firing in a coke shower.

The obtained tundish nozzle was used in a bloom continuous casting machine of company Z, and completed casting was completed after 3 charges in the same manner as the conventional gas-injection type tundish nozzle. Adhesion of inclusions to the inner wall was slight, and cost reduction was achieved because gas blowing was not necessary.

Example 3 Unstabilized zirconia 1 adjusted to a particle size of 100 μm or less
10 parts by weight and stabilized zirconia to parts by weight, 7 parts by weight of scaly graphite
To 5 parts by weight, 5 parts by weight of silicon carbide with a particle size of 100μ or less was added as an antioxidant, and 7 parts by weight of phenolic resin were added.
The mixture was mixed, formed into an immersion nozzle using a fuper press, and calcined in a coke shower.

When the obtained immersion nozzle was used in a continuous slab casting machine of both companies, complete casting was achieved in the same manner as conventional products using gas injection. Adhesion to the inner wall is slight, and there is less erosion than conventional products.
Furthermore, multiple series were also possible.

Furthermore, the addition of silicon carbide did not impair the effects of the present invention.

Table Buddha Example

Claims (1)

[Claims] Unstabilized zirconia with a weight ratio of 100 μ or less from 35 to
A continuous casting nozzle comprising 75% graphite, 5 to 15% graphite, and the remainder stabilized zirconia of 100 μm or less.