JPS6214507B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a casting nozzle for horizontal continuous casting that has excellent erosion resistance. In recent years, the vertical continuous casting method has replaced the vertical continuous casting method in which slabs are pulled downward from the bottom of a mold placed directly below the tundy, but the horizontal continuous casting method has been replaced by a horizontal continuous casting method in which slabs are pulled horizontally from a mold installed horizontally at the bottom of the side wall of the tundy. Continuous casting methods are being put into practical use because they require lower equipment costs than vertical continuous casting methods. The structure of a connecting portion between a tundish and a mold of a horizontal continuous casting machine for implementing the horizontal continuous casting method will be described with reference to the drawings. In the drawing, 1 is a tundish, 2 is a front nozzle horizontally attached to the lower side wall of the tundish 1, 3 is a mold horizontally attached to the front nozzle 2 via a casting nozzle, which will be described later, and 4 is a casting nozzle. . The casting nozzle 4 includes a feed nozzle 5 horizontally attached to the tip of the front nozzle 2 and a break ring 6 attached between the feed nozzle 5 and the mold 3. The molten steel contained in the tundish 1 is cast into a water-cooled mold 3 through a front nozzle 2 and a casting nozzle 4, where it is cooled and becomes an unsolidified slab. The unsolidified slab is intermittently pulled out from the mold 3 in the horizontal direction. The casting nozzle 4 receives a large thermal shock because it comes into direct contact with molten steel. For this purpose, it is conceivable to manufacture the casting nozzle with a sintered body of silicon nitride (Si ₃ N ₄ ), but although the silicon nitride sintered body has excellent thermal shock resistance, it has poor erosion resistance. . Erosion damage of casting nozzles mainly occurs when casting is performed for a long time or when high-oxygen steel with a high concentration of dissolved oxygen is cast. The cause of melting damage of the casting nozzle will be explained below. (1) Concerning melting loss during long-time casting: Generally, the concentration of dissolved Al in molten steel that is continuously cast is 0.01 to 0.02%, and the dissolved oxygen in molten steel determined by this is 3 to 8 ppm. . Therefore, the melting loss of Si ₃ N ₄ cast nozzles due to oxygen in the steel hardly occurs, and the melting loss of casting nozzles is mainly due to the Si in the Si ₃ N ₄ that makes up the casting nozzle being dissolved into the steel. It happens by doing. Nitrogen in Si ₃ N ₄ is partially dissolved in steel, but
Most of it becomes nitrogen gas and adheres to the surface of the casting nozzle as bubbles. This prevents molten steel from coming into direct contact with the surface of the casting nozzle to some extent, so compared to Si casting nozzles, Si ₃ N ₄
The corrosion rate of quality casting nozzles is slow. However, when casting is carried out for a long time, the
As mentioned above, Si in Si ₃ N ₄ dissolves into the steel, and the casting nozzle is damaged by erosion. (2) Concerning melting loss when casting high-oxygen steel: When the dissolved oxygen concentration in the steel is as high as 60 to 100 ppm, such as stainless steel, in addition to the melting loss mentioned in (1), the steel Added to this is corrosion damage due to dissolved oxygen inside. That is, when Si in Si ₃ N ₄ reacts with dissolved oxygen in steel, SiO gas is generated, and this gas
Escapes to the outside before becoming SiO ₂ . For this
Si ₃ N ₄ is melted away. From the above-mentioned viewpoint, the present invention provides a casting nozzle that is resistant to melting damage even when casting for a long time or when casting high oxygen steel. silicon powder within the range of 20 to 98% by weight and within the range of 2 to 80% by weight;
It is characterized in that it is formed by nitriding and sintering a cast nozzle molded body made of oxide powder of at least one of Cr ₂ O ₃ , TiO ₂ , and CaO in a nitrogen-containing atmosphere. Next, the reasons for limiting the components in this invention will be explained. The reason why the proportion of silicon powder as a raw material is set to 20 to 98% by weight is to maintain the strength of the nozzle when the molded body of the cast nozzle is nitrided. The reason why the proportion of the oxide powder of at least one of Cr ₂ O ₃ , TiO ₂ , and CaO as a raw material is set to 2 to 80% by weight is to improve the erosion resistance of the casting nozzle. That is, the purpose is to manufacture a casting nozzle that is not easily damaged by melting even when casting for a long time or when casting high oxygen steel. This will be explained in more detail. First, prevention of melting damage during long-term casting will be explained. In addition to Si ₃ N ₄ , when using a casting nozzle containing oxides that are difficult to dissolve in the molten steel, such as TiO ₂ , Si in the surface layer of the casting nozzle dissolves into the molten steel during casting, causing the surface layer of the nozzle to dissolve. is sintered _TiO2
A protective layer is formed. This protective layer can prevent Si ₃ N ₄ from dissolving. The oxide needs to be a compound that is not only difficult to dissolve in molten steel, but also cannot be reduced by components in the steel and is stable at an oxygen partial pressure that is in equilibrium with dissolved oxygen. Therefore, the above-mentioned oxide was used. For example, dissolved oxygen
When TiO ₂ is immersed in molten steel at 5 ppm, the saturated solubility of Ti is 0.56 ppm, which is hardly dissolved, while the saturated solubility of Ca in CaO is 0.03 ppm.
This is equivalent to not being dissolved. Next, prevention of corrosion damage when high oxygen steel is cast will be explained. In addition to Si ₃ N ₄ , TiO ₂ and CaO, which are difficult to dissolve in molten steel
When a casting nozzle containing such oxides is used, the protective layer is formed on the surface layer of the casting nozzle for the same reason as mentioned above. For this reason, even if high oxygen steel is cast, melting damage of the casting nozzle can be prevented. In addition,
Melting damage of the casting nozzle is also prevented for the following reasons. That is, when the amount of dissolved oxygen in molten steel increases, the saturation solubility of, for example, Ti and Ca decreases, making it difficult for these oxides to dissolve. These oxides present in the surface layer of the casting nozzle become the nucleus for SiO gas generated when Si ₃ N ₄ is oxidized to become SiO ₂ in the surface layer of the casting nozzle, and SiO ₂ is generated in the surface layer of the casting nozzle. more likely to be generated. Therefore,
This SiO ₂ is mixed in the protective layer and prevents melting damage of the casting nozzle. Next, embodiments of the invention will be described. The starting materials shown in Table 1 were adjusted to a predetermined particle size, an appropriate amount of a binder such as PVA was added and kneaded, and then dried to obtain a material for break ring.
After molding this raw material into the shape of a break ring using a press machine using a rubber press and a mold,
This molded break ring was prefired in an Ar atmosphere at 1200°C to remove the binder and the like. Then,
A break ring (product of the present invention) made of a silicon nitride composite sintered body was manufactured by firing the prefired break ring in a nitrogen gas atmosphere at 1000°C. This break ring was installed between the feed nozzle of a horizontal continuous casting machine and the mold, and a slab was cast by casting carbon steel with the components shown in Table 2. The amount of erosion was investigated. These results are shown in Table 3 together with the results obtained when a break ring made of Si as the starting material component and produced in the same manner as described above was used. The break ring erosion index is expressed as Dmm (break ring erosion amount)÷slab length (m)×100, and the smaller the value, the smaller the erosion loss amount. Table 4 shows the results when stainless steel with the components shown in Table 5 was cast in the same manner as above, and Table 6 shows the results when high chromium steel with the components shown in Table 7 was cast. Show the results.

【table】

【table】

【table】

【table】

【table】

【table】

[Table] As is clear from Tables 3, 5, and 7, the break ring of the present invention is effective even when casting is performed for a long time and when high-oxygen steel is cast.
It can be seen that the amount of erosion is extremely small compared to a break ring made only of Si. As explained above, the casting nozzle of the present invention provides extremely useful effects such as being extremely resistant to melting damage even when casting is performed for a long time or when casting high oxygen steel.

[Brief explanation of the drawing]

The drawing is a cross-sectional view showing the structure of the connecting portion between the tundish and the mold. In the drawings, 1...Tandateishu, 2...Front nozzle, 3
...Mold, 4...Casting nozzle, 5...Feed nozzle, 6...Break ring.

Claims (1)

[Claims] 1. Silicon powder in the range of 20 to 98% by weight and Cr ₂ O ₃ in the range of 2 to 80% by weight as raw materials,
For horizontal continuous casting with excellent erosion resistance, characterized in that it is made by nitriding and sintering a casting nozzle molded body made of oxide powder of at least one of TiO ₂ and CaO in a nitrogen-containing atmosphere. Casting nozzle.