JPH04231153A - Dipped nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To supply a dipped nozzle for continuous casting capable of preventing deterioration of the quality of a product by restraining alumina from sticking to each wall surface of an inlet part and a discharge outlet of a dipped nozzle used in the continuous casting of steel and the outer wall surface of a lower part side of a powder line, enabling a lot of times of continuous casting, drastically improving operating efficiency and preventing generation of phenomena that deposits peel, suspend in molten steel and are caught. CONSTITUTION:In the dipped nozzle for continuous casting of steel, a dipped nozzle for continuous casting is characterized by comprising the wall surface of the inlet part, the wall surface of the discharge outlet and/or the outer wall surface of the lower part of the main body till the powder line part of a refractory material of composition containing 10-50wt.% C, 10-30wt.% Ca, 35-80% zirconia, 0.1-10% calcium fluoride.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to an immersion nozzle for continuous casting that suppresses the adhesion of alumina on the inner hole of the immersion nozzle, the walls of the discharge hole, and the outer wall of the lower part of the powder line. It is related.

0002

BACKGROUND OF THE INVENTION Conventionally, Al2O3-C materials with high spall resistance, wear resistance and corrosion resistance have been frequently used as refractories for immersion nozzles, and ZrO2-C materials may also be used. However, when continuously casting molten steel, especially aluminum killed steel and aluminum silicon killed steel, using nozzles made of these materials, non-metallic inclusions such as alumina adhere to and grow on the inner hole of the nozzle and the wall of the discharge hole. Not only does the nozzle become clogged and casting becomes impossible, but the deposits peel off and become suspended in the molten steel, leading to deterioration in the quality of the resulting slab. In order to prevent such nozzle clogging, attempts have been made to blow inert gas such as argon gas or to use a nozzle made of ZrO2-CaO-C material as shown in JP-A-1-40154. .

0003

[Problems to be Solved by the Invention] However, with inert gas blowing, it is not possible to completely prevent alumina from adhering to the nozzle unless a large amount of gas is blown into the nozzle. Occurrence of entrainment or argon gas itself may cause product defects, leading to quality deterioration. In addition, even with a ZrO2-CaO-C nozzle, clogging occurs when gas blowing is stopped, so it is necessary to use it in combination with gas blowing from a source other than the immersed nozzle, and the above-mentioned quality deterioration occurs due to gas blowing. In addition, when replacing the ladle during continuous casting, the amount of alumina suspended in molten steel increases, and with the conventional amount of CaO, low melting point calcium aluminate (
(nCaO.mAl2O3), a sufficient effect of preventing alumina adhesion cannot be obtained.

0004

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention has developed a material that does not easily attract alumina even if the gas blowing is stopped or the amount of suspended alumina in molten steel increases. The gist of this is to provide a submerged nozzle for continuous casting of steel, in which the inner hole wall surface, the discharge hole wall surface, and/or the wall surface of the lower part of the main body up to the powder line portion has a weight of 10 to 50 wt. %C
, 10-30wt% CaO, 35-80% ZrO2
The present invention relates to a continuous casting immersion nozzle characterized in that it is made of a refractory having a composition containing 0.1 to 10% of CaF2.

[0005]

[Operation] CaO in the refractory reacts with alumina in molten steel to produce calcium aluminate. CaF2 is known as a slag slag agent, and has the function of lowering the melting point of oxides. ZrO2-CaO-CaF2-C containing this CaO and CaF2 in a stable state in the refractory
When used as a quality material for the nozzle inner hole and the partition wall surface of the discharge hole, CaO and CaF2 in the refractory react with alumina in the molten steel to produce a reaction product of CaO-Al2O3-CaF2. The reaction products are CaO and Al2
It has a lower melting point than calcium aluminate, which has the same O3 ratio and does not contain CaF2, and even a small amount of CaO can produce a low melting point substance even if a large amount of alumina is suspended in molten steel. This low melting point substance is washed away by the molten steel flow, causing slight erosion and renewal of the refractory surface to prevent adhesion.

[0006] The effect of CaF2 increases as the amount of CaF2 increases, and if it is less than 0.1 wt%, almost no effect is observed, but as the amount of CaF2 increases, corrosion resistance deteriorates. As a result of experiments, it is practically desirable that the amount of CaF2 be 10% or less.

[0007] In addition, alumina may adhere to the outer wall surface of the immersion nozzle and be captured by the molten steel. ZrO2- is also applied to the lower outer wall surface up to the
By using CaO-CaF2-C refractories, alumina in the molten steel and C in the refractories that have adhered to the molten steel can be removed.
A low melting point substance is generated with aO and CaF2 to prevent adhesion.

When C is less than 10%, heat spalling resistance is poor, and when it is more than 50%, erosion resistance is poor. ZrO2 and C
Although aO may be zirconia or lime, if we take into account the digestibility (easiness of weathering and disintegration due to reaction with water vapor, evaluated by the rate of decrease in compressive strength after autoclaving), all CaO sources should be supplied in the form of CaZrO3. It is desirable to use a ZrO2--CaO raw material which is electro-fused with 31% or less of CaO added thereto, either alone or in the form in which ZrO2 is added thereto.

[0009] This CaO reacts with alumina in molten steel to produce calcium aluminate. The higher the amount of CaO, the better; if it is less than 10%, less low melting point substances will be produced and sufficient effects will not be achieved. When CaO exceeds 27.6%, the amount excluding C and CaF2, that is, CaO and ZrO
Even if the largest amount of CaO
Practically speaking, it is desirable for CaO to be 30% or less, since it cannot be supplied in the form of CaZrO3 and the digestion resistance decreases.

[0010] Also, if ZrO2 is less than 35%, the corrosion resistance will deteriorate, so it is desirable to increase it, but if it exceeds 80%, the amount of CaO added will be less than 10%, at which a sufficient effect of CaO addition can be obtained. The following are desirable. The ZrO2-CaO-CaF2-C refractory in the present invention is
Generally, the above-mentioned electrofused ZrO2-CaO raw material, ZrO
2. It is obtained by adding phosphorous graphite to CaF2, etc., kneading with pitch, resin, etc. as a binder, shaping, drying, and firing in a non-oxidizing atmosphere. Furthermore, if necessary, it is also possible to combine metallic silicon to improve strength and silicon carbide to prevent oxidation and improve spall resistance.

[0011]

[Example] The inner hole wall surface, the discharge hole wall surface, the outer wall surface of the lower part of the main body up to the powder line portion (hereinafter referred to as the "required parts"), and other parts were constructed using a refractory made of a combination of the raw materials shown in Table 1. A submerged nozzle of the present invention was obtained. The properties of the refractories constituting this essential part are shown in Table 1 along with the properties of the refractories used in other parts and in comparative examples.

0012

[Table 1-1]

[0013]

[Table 1-2]

An example of an immersion nozzle obtained by constructing the necessary parts with the refractory thus obtained is shown in FIG.
Shown in Figure 2. Examples 1 to 6 In the immersion nozzle shown in FIG. 1, the upper part 5 of the main body is made of Al2O3.
-C refractory 7, powder line section 2 is made of ZrO2-C refractory 8, and the wall surface of inner hole section 1 and lower body part 4 including discharge hole 3 are made of raw materials shown in Examples 1 to 6 of Table 1. Contains Zr
It was composed of O2-CaO-CaF2-C refractory 6.

Embodiment 7 In the immersion nozzle shown in FIG. 2, the outer wall surfaces of the upper body side 5 and the lower body side 4 are made of Al2O3-C refractory 7, and the outer wall surface of the powder line section 2 is made of ZrO2-C refractory. 8, and the ZrO2-CaO-CaF2-C refractory 6 having the raw material composition shown in Table 1 was used only on the inner wall surface of the inner hole 1 and the wall surface of the discharge hole 3.

Comparative Examples 1 to 7 The nozzle in FIG. 3 has the same structure as that in FIG. The indicated ZrO2-CaO-C quality or ZrO
2-CaO-CaF2-C refractory 9.

Comparative Example 8 The nozzle shown in FIG. 4 is a conventional gas blowing type nozzle.
The upper body side 5 and the lower body side 4 are made of Al2O3-C refractory 7, and the outer wall side of the powder line section 2 is made of ZrO2-C.
A porous Al2O3-C refractory 10 is used for blowing Ar gas into the inner hole side.

1 by continuous casting using these nozzles.
250 tons of aluminum killed steel was continuously cast per pot. The operating conditions and results are shown in Table 2.

[0019]

[Table 2-1]

[0020]

[Table 2-2]

However, when eight pots were continuously cast using the nozzles of Examples 1 to 6 shown in FIG. Compared to the case where fewer nozzles are used, the amount of alumina deposited is smaller and the nozzle clogging index is smaller. This tendency becomes more pronounced as the amount of CaO increases and the amount of CaF2 increases.

In the immersion nozzle of Example 7 shown in FIG.
Since it is made of aF2-C refractory 6, it was possible to prevent alumina from adhering to the inner wall of the nozzle, but the lower part of the main body 4
Deposits were attached to 7 parts of the Al2O3-C refractories on the outer wall, deteriorating the product quality.

In Comparative Example 1, when the amount of alumina in the molten steel increased or the amount of Ar blown from the upper nozzle decreased, a nozzle clogging phenomenon due to alumina adhesion was observed, and the product quality deteriorated. Comparative Example 2 with a larger amount of CaF2 than the present invention range, Comparative Example 3 with a smaller amount of ZrO2, Comparative Example 5 with a larger amount of CaO, and Comparative Example 7 with a larger amount of C had less alumina adhesion but large melting loss in the inner hole. However, it is difficult to further extend the continuous casting time. Furthermore, in Comparative Example 6, which had a small amount of C, some nozzles broke at the start of casting. Comparative Example 4 was a case in which the amount of CaO was small and the amount of ZrO2 was excessive, and the alumina deposition was thick, a nozzle clogging phenomenon was observed, and the product quality deteriorated.

In Comparative Example 8 using the submerged nozzle shown in FIG. 4, when the flow rate of Ar was low, alumina adhered and the nozzle was clogged at the time of four-pan casting, resulting in a significant deterioration in quality. In addition, at a high Ar flow rate, alumina adhesion was reduced and nozzle clogging was alleviated, but Ar bubble defects were generated and product quality was significantly degraded.

[0025]

[Effects of the Invention] The nozzle according to the embodiment of the present invention uses a ZrO2-CaO-CaF2-C refractory material to prevent alumina from adhering to the molten steel in the parts that come into contact with the molten steel flow and the parts that are immersed in the molten steel. (1) Nozzle blockage due to alumina adhesion to the immersion nozzle can be avoided, making it possible to perform continuous casting many times in a row, significantly improving operational efficiency, (2) Adhesive products are peeled off and suspended in molten steel. (3) Since it is possible to prevent the phenomenon of turbidity and trapping, it is possible to prevent a deterioration in product quality due to this. (3) It is possible to eliminate Ar blowing, and it is possible to prevent the occurrence of defects caused by Ar bubbles. Effects such as this can be obtained.

[Brief explanation of the drawing]

[Figure 1]

FIG. 2 is a longitudinal cross-sectional view of a submerged nozzle that is an embodiment of the present invention.

[Figure 3]

FIG. 4 is a longitudinal cross-sectional view of a submerged nozzle of a comparative example.

[Explanation of symbols]

1 Inner hole portion 2 Powder line portion 3 Discharge hole 4 Lower body side 5 Upper body side 6 ZrO2-CaO-CaF2-C refractory 7
Al2O3-C refractory 8 ZrO2-C refractory 9 ZrO2-CaO-C refractory

Claims (1)

[Claims] [Claim 1] In a submerged nozzle for continuous casting of steel,
The inner hole wall surface, the discharge hole wall surface, and/or the outer wall surface of the lower part of the main body up to the powder line portion is 10 to 50 wt%.
of C, 10-30 wt% CaO, 35-80% Zr
A immersion nozzle for continuous casting, characterized in that it is made of a refractory having a composition containing O2 and 0.1 to 10% CaF2.