JPS6047223B2 - Manufacturing method of immersion nozzle for continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an immersion method for continuous casting in which molten steel is poured from a tundish into a mold in continuous steel casting. The present invention relates to a method for manufacturing a nozzle.

In continuous steel casting, when pouring molten steel from the tundish into the mold, oxidation of the molten steel being poured, turbulence of the molten steel,
Alternatively, in order to prevent the entrainment of slag and obtain good slabs, a submerged nozzle is used, the lower part of which is immersed in the molten steel in the mold.

On the other hand, mold powder is suspended on the surface of the molten steel in the mold for the purpose of preventing oxidation of the molten steel, acting as a lubricant between the mold and the molten steel, and trapping deoxidation products floating on the surface of the molten steel. A portion of the powder is melted into molten powder.

FIG. 1 is a schematic cross-sectional view showing a conventional immersion nozzle, where 1 is the immersion nozzle, 2 is the molten steel in the mold, and 3 is the molten powder.

As can be seen from the drawing, the immersion nozzle 1 has a part that contacts the molten steel 2 and a part that contacts the molten powder 3 in the mold, and a locally worn part 4 near the interface between the molten steel 2 and the molten powder 3. occurs. Such localized wear and tear determines the life of the submerged nozzle and, by extension, the tundish. As the above-mentioned immersion nozzle,
Conventionally used materials with high silica content and molten stone substance have moderate durability against molten powder, but if manganese is present in the molten steel, As a result of the reaction between the manganese component and the SiO2 component of the immersion nozzle material, the nozzle material was worn out, making it impossible to use it for a long time.

In addition, recently, alumina
A graphite nozzle material has been used, but this alumina-graphite nozzle material has the disadvantage of causing local wear at the interface between the molten steel and the molten powder in the mold as described above. Therefore, recently, zirconia-graphite immersion nozzle materials containing zirconia, an aggregate with excellent wear resistance at the interface between molten steel and molten powder, have begun to be used, but their durability remains unsatisfactory. It's not something you should do.

The present inventors have investigated the cause of localized wear in the zirconia-graphite nozzle material near the interface between molten powder and molten steel.

As a result, local wear and tear of the zirconia-graphite nozzle material
The molten powder penetrates into the part where the bonded carbon and graphite in the nozzle material disappear due to carburization into the molten steel, and the unbonded ZrO2 particles are transferred to the nozzle wall along with the particles. It was found that the cause was the repeated action of separating from the body. From the above, if a ceramic-bonded nozzle material is used, ZrO2 grains alone, which have excellent corrosion resistance against molten powder, will exhibit excellent performance in molten powder resistance and wear resistance near the interface between molten powder and molten steel. However, on the other hand, such a nozzle material in which a single ZrO2 grain is bonded to a ceramic has a drawback of poor spalling resistance.

Therefore, from the standpoint of spalling resistance, the presence of carbon, especially bonded carbon, is essential. As a result of further research into the above points, the present inventors have found that even if the bonded carbon and graphite in the nozzle material are carburized in molten steel, the zirconia aggregate in the carburized portion is bonded or sintered. It has been found that by forming a bond, the penetration of the molten powder into the carburized portion can be prevented, or even if the molten powder penetrates, the rate of wear of the nozzle material can be slowed down. The substance effective for assisting the bonding or sintering of the zirconia is silica (SiO2),
As a silica source, zircon (ZrO-SiO2) decomposition is also effective. I understood. This invention was made based on the above findings, and is based on the zirconia 6
5 to 95% by weight, graphite is 35% by weight or less, and particle size is 1.
0.01 to 1.5% of one or both of ultrafine silica (SiO2) or ultrafine zircon (ZrO2/JSlO2) of micron size or less, and a bond that becomes a carbon bond after reduction and firing. A compound in which not more than 1 weight percent of the agent is kneaded is placed at least in the part of the nozzle body that comes into contact with the molten mold powder layer on the surface of the molten steel, and after molding with an Isos 4 tactical press, it is fired in a reducing atmosphere. This method is characterized in that it is a method for manufacturing a continuous casting immersion nozzle.

Next, the reason why the composition range of the present invention is limited as described above will be explained.

If the zirconia content is less than 65% by weight, the corrosion resistance of zirconia will not be fully exhibited;
If it exceeds the weight percentage, it becomes impossible to effectively add silica or the like for firing the zirconia in the carburized portion, which will be described later.

Therefore, its content was determined to be 65 to 95% by weight. When the graphite content exceeds 35% by weight, wear and tear near the interface between the molten powder and the molten steel becomes significant.

Therefore, the upper limit of the content was set at 35% by weight. One or both of ultrafine silica (SjO2) or ultrafine zircon (ZrO2/SiO2) with a particle size of 1 micron or less to help sinter the zirconia in the carburized area.
If the content of seeds is less than 0.01% by weight, the dispersibility in the nozzle material will be insufficient and there will be no effect of including them. On the other hand, if the content exceeds 1.5% by weight, the corrosion resistance will deteriorate. do.

Therefore, its content was determined to be 0.01 to 1.5% by weight. In addition, the above-mentioned “silica (SlO2), zircon (Zr
The finer the powder, the larger the surface area of O2.SiO2), and the greater the possibility that it will exist between zirconia grains, thereby promoting the sintering effect between zirconia particles. On the other hand, if the particle size exceeds 1 micron, penetration into the spaces between the zirconia particles becomes insufficient, and the effect of aiding the sintering of zirconia cannot be obtained. Therefore, the particle size was determined to be 1 micron or less. Further, when the content of the binder exceeds 1% by weight, the carbon contained in the binder carburizes into the molten steel.

Therefore, the upper limit was set at 1% by weight. Next, the present invention will be explained using examples and a conventional example.

Example 1 Zirconia was 7% by weight, graphite was 14% by weight, and ultrafine silica (SiO2) of 1 micron or less was 0.0% by weight. Heel volume % and
After thoroughly kneading 6% by weight of the binder in the microwave and pitch, it was placed near the contact area with the molten powder layer in the nozzle body, molded using an isostatic press, and then heated to 1200% by weight in a reducing atmosphere. Calcined at a temperature of °C.

FIG. 2 shows a schematic vertical cross-sectional view of an example of the immersion nozzle manufactured as described above. In the drawings, reference numeral 5 indicates a nozzle body, and reference numeral 6 indicates a refractory layer having the above-mentioned composition, which is disposed near the contact portion with the molten powder layer. Example 2 Zirconia was 6% by weight, graphite was 2% by weight, ultrafine zircon of 1 micron or less was 1.2% by weight, and the total amount of resin and pitch as a binder was 6.5% by weight. After sufficiently kneading, the mixture was placed near the part of the nozzle body that came into contact with the molten powder layer, and then molded and fired in the same manner as in Example 1.

Example 3 92% by weight of zirconia, 0.5% by weight of graphite, 0
．． 0.05% by weight of ultrafine silica powder of 0.04 microns or less, and 6.5% by weight of resin and pitch as a binder.
After thorough kneading, the mixture was placed in the vicinity of the contact area with the molten powder layer in the nozzle body, and this was molded and fired in the same manner as in Example 1.

Conventional Example 1 After sufficiently kneading 8 mass% of zirconia, 14% by weight of graphite, and 6% by weight of resin and pitch as a binder, the mixture was mixed in the vicinity of the contact area with the molten powder layer in the nozzle body. This was molded and fired in the same manner as in Example 1.

Table 1 shows the physical properties of the refractory layer located near the contact area with the molten powder in the immersion nozzles of Examples 1 to 3 and Conventional Example 1, and the immersion nozzles used in actual continuous casting. It shows the results of using it and examining its wear and tear rate. As is clear from Table 1 above, when the immersion nozzle manufactured by the method of the present invention is used, the wear rate is reduced by about 40% compared to the conventional immersion nozzle, and the service life is greatly extended. was completed.

As described above, according to the present invention, there is less occurrence of local wear, especially near the interface between molten steel and molten powder in the mold, and the service life is greatly extended compared to conventional immersion nozzles. Since the contained silica and zircon are ultrafine powders, excellent industrial effects are brought about, such as promoting the sintering effect between zirconia.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing a conventional submerged nozzle, and FIG. 2 is a schematic cross-sectional view showing a submerged nozzle to which the present invention is applied. In the drawings, 1... conventional immersion nozzle, 2...
... Molten steel, 3... Molten powder, 4...
. . . Locally worn portion, 5 . . . Main body of the immersion nozzle of the present invention, 6 . . . Refractory layer disposed in the contact portion with the molten powder layer.

Claims (1)

[Claims] 1 65 to 95% by weight of zirconia, 35% by weight or less of graphite, and ultrafine silica (Si) with a particle size of 1 micron or less.
O_2) and ultrafine zircon powder (ZrO_2・SiO_
0.01 to 1.50% by weight of at least one of 2);
Then, 13% by weight of a binder that becomes a carbon bond after reduction firing.
The following are kneaded, the resulting mixture is placed at least in the part of the nozzle body that comes into contact with the molten mold powder layer on the surface of the molten steel, and is molded using an isostatic press, and the resulting molded product is placed in a reducing atmosphere. 1. A method for manufacturing a continuous casting immersion nozzle, characterized by firing the immersion nozzle.