JPH05318060A - Molten metal supplying nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To stably prevent the clogging of a molten metal supplying nozzle in long time. CONSTITUTION:On the flowing passage wall in the inner part of the molten metal supplying nozzle 1, coating agent 2 containing >=20wt% SiO2 is applied. Further, at the time of coating this coating agent, a gap is arranged and by directly contacting this refractory with the atmosphere, decarburized layer is developed during preheating of the nozzle 1, and by developing the low m.p. oxide layer, the clogging of nozzle can stably be prevented in long time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an immersion nozzle for continuous casting, which prevents inclusion particles suspended in the molten metal in the nozzle from accumulating in the nozzle flow path,
It is possible to improve the production capacity of the continuous casting process.

[0002]

2. Description of the Related Art In the continuous casting method, when molten metal (molten metal, hereinafter referred to as molten steel for steel) is supplied from a molten steel ladle (hereinafter referred to as pot) to a tundish or from a tundish to a mold. , Through a molten steel feed nozzle made of refractory. At this time, minute inclusion particles suspended in the molten steel are deposited on the inner wall of the refractory, so that the molten steel flow passage is narrowed, so-called nozzle clogging occurs. Hereinafter, the clogging phenomenon of the molten steel supply nozzle will be described with respect to the immersion nozzle used for supplying the molten steel from the tundish to the mold.

Conventionally, as a mechanism of nozzle clogging,
As disclosed in JP-A-57-27967, a group of inclusions in which a mesh-like alumina layer formed by a chemical reaction between a refractory and molten steel is used as a starting point and a large number of fine inclusion particles are united on it. It is said that the main cause is the solidification, adhesion, and deposition of molten steel containing iron. As one means to prevent nozzle clogging, the SiO ₂ content in the refractory, which is the cause of the formation of the reticulated alumina layer, is reduced. It has been proposed that it is effective.

However, even when the formation of the mesh-like alumina layer is effectively prevented, the alumina particles suspended in the molten steel directly constitute the refractory when the casting time is as long as 200 minutes or longer. There is a problem that nozzle clogging occurs because further suspension alumina particles are deposited starting from the point of contact with the oxide particles that form and adhere to the inner wall of the nozzle.

In order to prevent the accumulation of such alumina particles, for example, as disclosed in Japanese Patent Laid-Open No. 1-40154, CaZrO ₃ (hereinafter referred to as ZCG) is contained in a refractory material and deposited. Attempts have been made to prevent the clogging of the nozzles by lowering the melting point of the alumina particles to be washed away. However, even when using a ZCG quality refractory, if the melting point of the boundary between the refractory and the deposit is not sufficiently lowered and it is in a solid state during casting, the deposition of alumina particles proceeds as in the conventional case. However, nozzle clogging similarly occurs. As described above, none of the conventional methods is capable of stably preventing the deposits in the molten metal supply nozzle for a long period of time and continuing stable casting work.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the limitation of the continuous casting ratio in continuous casting and improves the productivity, as in the prior art, without the generation of deposits in the molten metal supply nozzle. Is an issue.

[0007]

The present invention is a molten metal supply nozzle for continuous casting, which solves the above problems. 1. A coating agent containing 20 wt% or more of SiO ₂ is applied on the inner wall surface of the molten metal supply nozzle for continuous casting made of zirconia lime. The molten metal supply nozzle for continuous casting is characterized in that when the coating agent is applied on the wall surface of the nozzle internal flow path, a gap is provided in a part of the coating agent.

[0008]

The operation of the molten metal supply nozzle of the present invention will be described below. The present inventors carried out a detailed investigation and observation of deposits formed and accumulated mainly in the molten metal supply nozzle and the immersion nozzle. A schematic diagram of this observation result is shown in FIG. The material of the immersion nozzle 1 is alumina graphite (hereinafter referred to as AG), the average deposits 3 and 4 have a thickness of about 20 mm, and the appearance is a portion 3 mainly composed of solidified metal, It can be classified into a part 4 mainly composed of brick-like powder.

Next, the results of observing each of the deposit 3 mainly composed of metal and the deposit 4 mainly composed of brick-like powder in an enlarged manner are shown in FIGS.
Each is shown schematically. As shown in FIG. 3, the deposit 3 mainly composed of metal is a solidified metal containing a large number of fine inclusion particles 6 on the mesh alumina layer 5 as a starting point, as in the conventional observation result. It is configured. Further, while immersing the deposit 3 in oxalic acid to energize the metal portion to dissolve the metal having a depth of 0.2 mm from the surface of the sample and expose only the inclusion particles 6, the inclusion particles 6 were observed. It was confirmed that they were bonded to each other and formed a sponge fibrous network as a whole.

This is different from the case shown in FIG. 3 in that the metal 7 is distributed in a granular form even in the deposit 4 mainly composed of inclusion particles, as shown in FIG. The network was observed as in FIG. Furthermore, as a result of an observation focusing on the individual alumina inclusion particles forming these networks, the chemical composition of the individual inclusion particles is alumina, and their morphology is in the tundish or product cast. It was confirmed to be the same as the contained alumina particles. From the above survey results, the nozzle deposits 3 and 4 are those in which alumina particles suspended in molten steel in advance are deposited and deposited on the inner wall of the nozzle to form a network, which causes nozzle clogging. There was found.

Next, casting was performed using a nozzle refractory material of ZCG quality, but since the same nozzle clogging as that of AG quality occurred, the same deposits as above were investigated. The structure of the deposit itself is the same as that shown in FIGS. 3 and 4,
No formation of reticulated alumina layer 5 was observed and instead of Al
₂ O ₃ (66 wt%)-ZrO ₂ (4 wt%)-CaO
An oxide layer of (30 wt%) was formed. It is known that the melting point of the oxide having such a chemical composition is about 1600 ° C., and it was confirmed that the oxide adhered in a solid state even during casting.

That is, it has been found that the boundary layer of the deposit and the refractory does not liquefy, which is the principle of preventing nozzle clogging of the ZCG nozzle. From the above analysis results, the nozzle deposits 3 and 4 are generated mainly because the inclusion particles 6 in the molten steel form a sponge-like network, and when the ZCG quality nozzle is used. However, we have found a new finding that nozzle clogging occurs when a layer of high melting point oxide is formed on the inner wall of the nozzle.

That is, a network of inclusion particles 6 is formed, and in order to adhere to the inner wall of the nozzle, an oxide layer serving as an origin of the adhesion is required. Even if the oxide layer serving as the adhesion starting point is a solid during casting, nozzle clogging similar to that of the AG nozzle occurs even when the ZCG nozzle is used. However, in order to effectively exert the effect of preventing clogging of the ZCG nozzle, it is necessary to form a liquid oxide layer on the inner wall of the nozzle from the start of casting and continuously create this liquid layer during casting. The conclusion was reached and the molten metal supply nozzle of the present invention was completed.

That is, in order to create a liquid oxide layer on the inner wall of the nozzle at the start of casting, a coating agent containing SiO ₂ as a main component is applied to the inner wall of the nozzle, and preheating before casting is performed. Immediately before casting, SiO ₂ was formed on the inner wall of the nozzle.
Previously created a low-melting liquid oxides -ZrO ₂ -CaO system. By starting the casting in this state, the generation of the deposit starting point due to the accumulation of the inclusion particles at the initial stage of casting is effectively prevented.

On the other hand, as casting progresses, the liquid layer created during preheating gradually increases in alumina and changes to a high melting point oxide, so that the liquid state is maintained during casting. Is ZrO ₂ and CaO from inside the refractory
Need to continue to supply. For this purpose, a flow path for moving ZrO ₂ and CaO from the inside of the refractory to the inner wall is required.

In the conventional ZCG nozzle, an antioxidant is applied to the entire inner wall of the nozzle, and the graphite of the refractory is not oxidized during the preheating and is densely packed, so that ZrO ₂ and CaO move. There is no flow path to do this. Therefore, when casting is continued for a long time with ZCG quality, a solid oxide layer is formed on the inner wall of the nozzle due to the adhesion of the suspended alumina, and nozzle clogging occurs.

However, in the case of the molten metal supply nozzle of the present invention, a part of the coating agent applied to the inner wall of the nozzle is a void, and the refractory and the atmosphere are in direct contact with each other. A decarburized layer is created in which the graphite in the refractory is oxidized to become CO gas and disappear. Therefore, the part where the graphite has disappeared becomes a flow path for the movement of ZrO ₂ and CaO from the inside of the refractory to the inner wall, and the melting point of alumina particles adhering to the inner wall one after another continuously decreases during casting. Therefore, even when casting is performed for a long time, nozzle clogging is effectively and stably prevented.

On the other hand, when the coating material is applied without forming voids on the entire inner wall of the nozzle, the melting point is lowered only on the inner surface of the nozzle, but the low melting layer flows out as the casting proceeds. However, since decarburization does not occur during preheating and the refractory is densely packed, ZrO ₂ from inside the refractory,
Since CaO cannot move and is not supplied to the surface, the adhesion immediately after the start of casting is prevented, but when the casting time becomes long, the alumina particles are deposited and the nozzle is clogged.

[0019]

EXAMPLES Examples of the molten metal supply nozzle of the present invention will be described below with reference to operation examples and comparative examples using the same. On the inner wall of the ZCG substance nozzle 1 as shown in FIG. 1, four kinds of coating agents 2 of A to D having the chemical composition as shown in Table 1 are provided.
Is applied by a manual brush coating in a grid pattern so that the nozzle refractory has a portion 10 in direct contact with the atmosphere, and the same brush coating is applied to the entire inner wall with an antioxidant at a uniform thickness. The nozzle refractory and the one in which the atmosphere did not come into direct contact were preheated under the same conditions.

[0020]

[Table 1]

FIG. 5 shows a comparison of the state of the inner wall of the nozzle after preheating. In the conventional nozzle, which was uniformly coated with the antioxidant, no low melting point and liquefied layer was observed on the refractory material densely filled with graphite.
On the other hand, among A, B, and C in Table 1 of the method of the present invention, in which the coating agent was applied in a lattice pattern on the inner wall of the nozzle, graphite in the refractory disappeared on the entire inner wall of the nozzle, resulting in porous desorption. A coal layer 9 was created with a thickness of about 3 mm, and a layer having a low melting point and being liquefied was observed thereon.

Next, comparative casting was carried out by a two-strand continuous casting machine using both the conventional nozzle and the nozzle of the present invention, and the growth state of deposits 3 and 4 in the immersion nozzle after casting was observed. did. At the time of casting, the extremely low carbon steel type molten steel of the composition system shown in Table 2 was cast by continuous casting of 4 pots. The casting speed was 1.4 m / min, which was constant during casting, the total amount of molten steel cast was 1440 tons, and the total casting time was 150 minutes.
The cross-sectional size of the product slab manufactured at this time is 28.
It is 0 mm (thickness) × 1830 mm (width).

[0023]

[Table 2]

FIG. 6 shows the state of formation of the deposits 3 and 4 in the immersion nozzle, which was investigated after casting and was compared between the conventional method and the method of the present invention. In the conventional method, deposits 3 mainly consisting of inclusion particles 6 having a thickness of 10 to 20 mm are produced and attached on the inner wall of the dipping nozzle 1 and the radius of the nozzle internal flow channel is significantly narrowed. Rod pecking (mechanical removal of deposits inside the dipping nozzle from above the tundish with a long iron rod) is performed.

On the other hand, in the nozzle in which the coating agents of the components A, B, and C in Table 1 of the present invention are applied in a grid pattern, there is no generation of deposits 3 in the nozzle, and abnormal operation such as stick plucking occurs. Was also not implemented. Further continuous casting using the method of the present invention,
Even when the molten steel amount was increased to 5300 tons, there was no generation of deposits 3 in the immersion nozzle 1, and in the conventional method, only 1440 tons at maximum could be continuously cast due to insufficient molten steel supply due to nozzle clogging. , It has become possible to greatly improve its casting productivity.

In this embodiment, the case where the composition shown in Table 1 is mainly used as the material of the coating agent is described.
It is not necessary to specify the chemical composition of the coating material as long as it contains 20 wt% or more of SiO ₂ .
Further, the coating thickness of the coating agent is not specified, and a coating amount of about 0.1 to 1.0 mm may be applied in an amount sufficient to form a liquid layer at the end of preheating.

Further, the coating method of the coating agent in the present embodiment has been described in the case where the coating is applied in the form of a grid by manual brush coating, but the coating method is not specified, and for example, it can be uniformly applied to the entire inner wall. After coating, peel off the coating agent with a needle or the like to make the refractory and the atmosphere in direct contact, or apply the coating agent in a staggered manner to create voids for creating a decarburized layer. It is preferable to make it evenly distributed over the entire inner wall of the nozzle.

[0028]

As described above, the molten metal supply nozzle of the present invention can effectively prevent nozzle clogging caused by the accumulation of inclusion particles generated in the nozzle. Therefore, the upper limit of the continuous casting ratio, which has been conventionally limited by nozzle clogging, can be eliminated, and the productivity of the continuous casting process can be significantly improved.

[Brief description of drawings]

FIG. 1 (a) shows a coating state of a coating agent in a nozzle of the present invention. (B) Shows the coating state of the coating agent in the conventional nozzle.

FIG. 2 shows a state in which a deposit in a nozzle is generated by a conventional nozzle.

FIG. 3 is an enlarged view of a metal-based deposit.

FIG. 4 is an inclusion-based deposit.

FIG. 5 is a diagram showing a state of the inner wall of the nozzle at the end of preheating. (A) Inventive nozzle (b) Conventional nozzle

FIG. 6 is a diagram showing a comparison of a state of deposit formation between the nozzle of the present invention and the conventional nozzle. (A) Inventive nozzle (b) Conventional nozzle

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Immersion nozzle 2 Coating agent 3 Voids 4 Inclusion-based deposits 5 Metal-based deposits 6 Alumina inclusion particles 7 Metals 8 Reticulated alumina layer 9 Decarburized layer and low melting point oxide layer 10 Nozzle refractory is in direct atmosphere Contact part

Claims (2)

[Claims] 1. SiO ₂ is formed on the wall surface of an internal flow path of a molten metal supply nozzle for continuous casting made of zirconia lime.
A molten metal supply nozzle for continuous casting, characterized in that a coating material containing at least wt% is applied. 2. The molten metal supply nozzle for continuous casting according to claim 1, wherein when the coating agent is applied on the wall surface of the nozzle internal flow path, a gap is provided in a part of the coating agent.