JPS621345B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a firing nozzle for continuous casting, such as a highly corrosion-resistant immersion nozzle. Conventional nozzles, such as immersion nozzles, are known to have a structure in which a ring made of zirconia or zircon-graphite refractory material is placed in the slag line part of the alumina-graphite nozzle body, which requires corrosion resistance. There is. However, such immersion nozzles have the following problems. Zircon ( _ZrO2 .
Zircon (SiO ₂ ) is inexpensive, but its corrosion resistance is limited due to its low ZrO ₂ content of approximately 67%. Baddellite (natural mineral) as a source of zirconia
When using zirconia or desiliconized zirconia, these are relatively inexpensive, have a high ZrO ₂ content, and have higher corrosion resistance than zircon, but due to poor sinterability of particles, carbon elution occurs during use. If this occurs, particles will fall off, resulting in a decrease in corrosion resistance. When stabilized zirconia is used, it has a high ZrO ₂ content and good sinterability, so it is almost satisfactory in terms of corrosion resistance, but it is very expensive and it is difficult to reduce nozzle cost. The present invention was made in view of the above circumstances, and it is an object of the present invention to provide a firing nozzle for continuous casting that is inexpensive and has high corrosion resistance. That is, the present invention provides a zirconia source with a zirconia content of 80% or more consisting of zirconia, baddellite, desiliconized zirconia alone or a mixture of two or more selected from zirconia, baddellite, desiliconized zirconia, and zircon in terms of weight ratio. 94%, carbon 5
This is a firing nozzle for continuous casting consisting of ~39% and 1~35% of magnesia or calcia. The zirconia source used in the present invention contributes to improving the corrosion resistance of the nozzle. The reason why the zirconia content in the zirconia source is limited is that if the content is less than 80%, a large amount of low melting point substances will be produced by reaction with magnesia or calcia, making it impossible to expect improvement in corrosion resistance. In addition, the reason why the amount of the zirconia source was limited to the above range is that if the amount is less than 60%, corrosion resistance cannot be sufficiently improved, whereas if it exceeds 94%, it tends to get wet with steel and slag. This is because it becomes more prone to melting damage. The carbon used in the present invention improves the spalling resistance of the nozzle and makes it difficult to wet with molten steel and slag. Examples of such carbon include natural graphite, artificial graphite, coke, and carbon black. However, from the viewpoint of improving spalling resistance, it is desirable that 50% or more of the amount of carbon blended be natural graphite. The reason for limiting the blending ratio of carbon to the above range is that if the amount is less than 5%, the effect of adding carbon cannot be expected to be sufficient, whereas if it exceeds 39%, carbon elution into the molten steel becomes obvious, resulting in corrosion resistance. This is because it leads to a decline in sexuality. The magnesia or calcia used in the present invention functions to prevent zirconia particles from falling off during use of the nozzle. That is, magnesia and calcia form a solid solution with zirconia and help sinter the zirconia particles together during use of the nozzle.
Furthermore, since the melting point (softening point) does not drop significantly, zirconia is prevented from falling off even after the surrounding carbon is eluted into the molten steel. The magnesia or calcia source may be any compound such as carbonate, as well as Mg or Ca oxides, as long as it is converted into an oxide during firing or use. The reason why the blending ratio of magnesia and calcia is limited to the above range is that if the amount is less than 1%, the effect cannot be fully expected, whereas if it exceeds 35%, corrosion resistance will decrease due to their erosion. It is. The firing nozzle for continuous casting of the present invention can be manufactured, for example, by the following method. First, the zirconia source mentioned above in terms of weight ratio is 60 to 94.
%, carbon 5-39% and magnesia or calcia 1-35%, a binder is added and kneaded. The binder is not particularly limited as long as it does not significantly lower the melting point (softening point) of the matrix, but organic binders such as tar pitch and resins, and inorganic binders such as phosphates may be used. desirable. However, the organic binder is 5 to 30 parts by weight per 100 parts by weight of the raw material powder, and the inorganic binder is 5 to 30 parts by weight per 100 parts by weight of the raw material powder.
It is desirable to add 10 parts by weight or less per 100 parts by weight. Subsequently, the kneaded product is molded, preferably by a rubber press (isostatic press) capable of making the characteristics of the molded product uniform, and then fired to produce a fired nozzle for continuous casting. Next, examples of the present invention will be described. Examples 1 to 8 and Comparative Examples 1 to 4 A predetermined binder as shown in the table was added to the raw material powder with the blending ratio shown in the table below, and after molding with a rubber press, it was baked at 1300°C and 12 types of immersion were made. Got the nozzle. The bulk specific gravity, apparent porosity, compressive strength, spalling property, erosion rate, and charge number in a practical test of the obtained immersion nozzles (including comparative examples) were investigated. The results are also listed in the same table. The spalling properties are the results obtained when a cylindrical sample with an inner diameter of 70 mm, an outer diameter of 130 mm, and a length of 200 mm was rapidly heated to 1400°C and cooled with water, which was repeated twice. The melting loss rate is the melting loss speed when ss412kg and powder 0.2kg are melted in a crucible and a 20φ x 100mm sample is immersed for 1 hour. The practical test was evaluated by the number of charges when ordinary steel was continuously cast using a 250 ton ladle. In addition, two layers in the table are those in which the nozzle body is made of alumina graphite and a ring-shaped refractory material with the composition shown in the table is provided in the slag line, and the single layer is made of only the refractory material with the composition in the table. It is what was done.

【table】

[Table] As is clear from the above table, the immersion nozzle of the present invention has much better corrosion resistance than the conventional nozzle.
It can be seen that the number of charges in the practical test can be increased by that much, that is, the durability can be improved. The firing nozzle for continuous casting of the present invention can also be used as a long nozzle connecting a ladle and an ingot to achieve the same effect as the bottom pouring method.

Claims (1)

[Claims] 1 Zirconia source with a zirconia content of 80% or more consisting of zirconia, baddeleyte, desiliconized zirconia alone or a mixture of two or more selected from zirconia, baddeleyte, desiliconized zirconia, and zircon in a weight ratio of 60 to 94%, carbon A firing nozzle for continuous casting having a composition of 5 to 39% and 1 to 35% of magnesia or calcia.