JPH09239504A - Submerged nozzle for continuous casting of steel containing high oxygen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the spalling resistance by using a porous refractory not containing carbon at a part of a submerged nozzle in contact with the molten steel to suppress oxidation of carbon in the refractory to constitute a nozzle body by the oxygen in the molten steel during the casting. SOLUTION: A surface of a part of a submerged nozzle in contact with the molten steel is covered with the porous refractory made of carbide and/or non-oxide. The porous refractory is 20-60% in apparent porosity, 0.02-0.5mm in mean diameter of pores, and 2-10mm in covering thickness. The conventional method such as the mechanical forming method, the rubber press method, and the slip cast method can be used as the manufacturing method of the submerged nozzle. The binder to be added which is required during the manufacture is not specially limited, and the binder such as the sodium silicate, aluminum phosphate, phenol resin, and CMC may be accepted.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a dipping nozzle for continuous casting of high oxygen content steel.

[0002]

2. Description of the Related Art High oxygen content steel is widely used as a base metal material for enamel. Compared to plain carbon steel, this grade has the following two characteristics: The oxygen content of plain carbon steel is about 20 ppm, whereas that of high oxygen content steel is as high as 200-600 ppm, which is significantly higher. Most of the oxygen in ordinary carbon steel exists in the form of oxide inclusions such as Al ₂ O ₃ , but most of the oxygen in high oxygen content steel exists in a dissolved state, and the oxide inclusions are very small. .

In continuous casting of high oxygen content steel, an alumina refractory material containing 20 to 30% by weight of carbon is generally used as a dipping nozzle used for introducing molten steel from a tundish into a mold. Has been done. The purpose of using the carbon-containing refractory is to increase the thermal conductivity of the refractory and improve the spalling resistance. However, when casting molten steel, carbon (C) in the nozzle is
Oxidation to dissolved oxygen ( O 2 ) in the molten steel occurs by the following reaction occurring at the interface between the nozzle inner tube and the molten steel:

## STR1 ## C + O 2 = CO (g) As a result, the structure of the nozzle surface becomes brittle and is washed away by the molten steel flow, which damages the nozzle and reduces the durability.

On the other hand, in Japanese Patent Laid-Open No. 62-212284, 100 parts by weight of an antioxidant mainly composed of silicon carbide whose melting point is adjusted to 300 ° C. to 1500 ° C. and low melting point glass is mixed with 2 parts of zirconia fine powder. 50 parts by weight was added to the mixture to make inorganic,
Alternatively, a method for preventing oxidation of a zirconia-carbon material, which is characterized in that a coating agent in the form of a slurry or a paste is obtained by adding an organic solution to the surface of the zirconia-carbon material refractory, is proposed, There are the following problems: The antioxidant layer easily cracks and peels off during drying, and it is difficult to form a uniform glass coating film. When the phase of the low melting point glass comes into contact with hot molten steel, it melts,
It will not flow down and will not function to prevent oxidation.

Further, Japanese Utility Model Application Laid-Open No. 2-38153 discloses a technique in which a portion of a nozzle which is in contact with molten steel and a refractory material of a nozzle body are separated. Further, Japanese Utility Model Publication No. 63-3732 discloses a technique (a refractory material is divided) in which a powder sleeve portion of a main body of an immersion nozzle is provided with a protective sleeve. However, these nozzles are not intended for immersion nozzles for continuous casting of high oxygen content steel, and are not sufficient for preventing nozzle damage due to oxidation of carbon by oxygen in molten steel.

[0006]

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a submerged nozzle for continuous casting of high oxygen content steel which prevents damage caused by oxidation of carbon by oxygen in molten steel.

[0007]

That is, the present invention relates to a continuous casting immersion nozzle used for injecting molten steel from a tundish into a mold, and a porous refractory material is provided at a portion of the immersion nozzle which is in contact with the molten steel. The present invention provides a submerged nozzle for continuous casting of high oxygen content steel, characterized in that

[0008]

DETAILED DESCRIPTION OF THE INVENTION Generally, the spalling resistance of a refractory material depends on the porosity of the refractory material itself. FIG. 1 shows the relationship between the porosity and the spalling resistance index of various materials measured and tested. First, mix each raw material in a predetermined mixing ratio,
After kneading, 230 × 114 at 1800 kg / cm ² pressure
It is pressed into a size of × 65mm, and this molded body is
A sample was prepared by baking at 00 ° C. for 10 hours. Test is 40x40x pre-fired at 1000 ° C
It was carried out by the method "reference: refractory material 44 [2] 75 (1992)" for quantifying the number of cracks generated when a 230 mm sample was immersed in molten steel at 1650 ° C according to a certain rule. Figure 1 shows the numerical results.

From FIG. 1, in both cases of Al ₂ O ₃ and MgO, the spalling resistance is significantly improved as the porosity increases up to 50%, and the spalling resistance decreases as the porosity further increases. I understand that Further, from FIG. 1, in the porosity range of 20 to 60%, the spalling resistance of Al ₂ O ₃ or MgO is the spalling resistance of the Al ₂ O ₃ refractory containing 25% by weight of carbon. It turns out that it is about the same as sex.

Based on the above findings, the present invention provides that when a porous refractory material is used on the molten steel side of a continuous casting immersion nozzle made of a carbon-containing refractory material, the porosity of the porous refractory material should be controlled appropriately. , Its spalling resistance is not considered to be a problem. In the high oxygen content steel, since Al ₂ O ₃ inclusions existing in ordinary carbon steel are very small as described above, when molten steel passes through the immersion nozzle, the inclusions are formed in the immersion nozzle inner pipe. There is no risk of adhesion and blockage of the nozzle.

The porous refractory materials are Al ₂ O ₃ , MgO, Zr.
It may be composed of an oxide such as O ₂ or SiO ₂ and a non-oxide such as AlN or SiC, or a mixture thereof.

Further, since the wettability between the molten steel and the refractory is very poor, if the size of the pores in the porous refractory is small to some extent, the molten steel penetrates into the pores due to static pressure and oxidizes carbon in the nozzle body. There is no possibility of doing it. According to the result of the actual machine test, it is desirable that the average pore diameter is in the range of 0.02 to 0.5 mm. If the average pore diameter is less than 0.02 mm, the sponge resistance of the porous refractory material is deteriorated, which is not preferable, and if the average pore diameter exceeds 0.5 mm, the surface strength becomes weak and the durability is poor. It is not preferable because it decreases.

Further, as a result of examining the relationship between the used thickness of the porous refractory and the casting time by an actual machine test, it was found that the used thickness should be about 2 to 10 mm. If the thickness used is less than 2 mm, the castable time becomes short, which is not preferable, and if it exceeds 10 mm, the castable time does not significantly increase, and the manufacturing cost of the permeation nozzle increases. Not preferable.

As a method for producing the immersion nozzle for continuous casting of the present invention, a conventional method such as a mechanical molding method, a rubber pressing method, a slip casting method or the like can be used, and a binder required at the time of production is Without limitation, sodium silicate, aluminum phosphate, phenolic resin, CMC
Conventional binders such as can be used.

[0015]

EXAMPLES The immersion nozzle for continuous casting of high oxygen content steel of the present invention will be further described below with reference to examples. Example 1 An immersion nozzle for continuous casting of the product of the present invention having the structure shown in FIG. 2 was produced. Here, the material of the main body is 50% by weight of Al ₂ O ₃ ,
A refractory material composed of 25% by weight of SiO _{2 and} 25% by weight of C, and the porous refractory material is 80% by weight of Al ₂ O ₃ and SiO 2.
It consists ₂ 20 wt%, a porosity of 35%, the pore average diameter 0.
The thickness used was 3 mm, and the thickness used was 7 mm. The immersion nozzle had the structure shown in FIG. 2 by the rubber press method (the inner diameter of the nozzle inner tube was 100 mm, the outer diameter of the nozzle was 160 mm, and the height was 700 mm).

Example 2 95% by weight of Al ₂ O ₃ and SiO ₂ were used as the porous refractory material.
5% by weight, porosity 45%, average pore diameter 0.1
mm, except that the thickness used is 7 mm,
A dipping nozzle for continuous casting of the product of the present invention was produced by the same method as in Example 1.

Example 3 As a porous refractory material. 70% by weight of Al ₂ O ₃ and MgO ₃
0% by weight, porosity 50%, average pore diameter 0.0
An immersion nozzle for continuous casting of the product of the present invention was produced in the same manner as in Example 1 except that the thickness was 8 mm and the thickness used was 7 mm.

Comparative Example 1 As a material for the immersion nozzle, 50% by weight of Al ₂ O ₃ , 25% by weight of SiO _{2 and} 25% by weight of C were used, and a comparative product having the configuration shown in FIG. 3 was immersed for continuous casting. A nozzle was produced.

The product 1 of the present invention produced as described above
Nozzle durability was evaluated by examining the inner tube damage of Nos. 2 and 3, and Comparative Immersion Nozzles. In addition,
The test was C: 0.02% by weight, Mn: 0.31% by weight,
P: 0.008% by weight, S: 0.017% by weight, O: 57
A high oxygen content steel having a composition of 9 ppm was used and the molten steel temperature was 1562 ° C. The relationship between the obtained casting time and the melting loss of the inner pipe is shown in FIG.

As can be seen from FIG. 4, the melt loss rate of the comparative product is 4 mm / hour and the casting time is 1.5 hours, whereas the melt loss rate of the product 1 of the present invention is 1.5 mm / hour. In terms of time, the castable time was 4 hours, the melt loss rate of the product 2 of the present invention was 1.2 mm / hour, and the castable time was 5 hours. Further, the erosion rate of the product 3 of the present invention is 1.0 mm /
In terms of time, the castable time was 6 hours. That is, it was confirmed that the durability of the immersion nozzle for continuous casting was significantly improved by using the product of the present invention.

[0021]

INDUSTRIAL APPLICABILITY In the immersion nozzle for continuous casting of high oxygen content steel according to the present invention, by using a carbon-free porous refractory material in the portion of the immersion nozzle that is in contact with molten steel, oxygen in the molten steel during casting Damage to the refractory material due to oxidation of carbon in the refractory material forming the immersion nozzle body can be significantly suppressed, which enables continuous casting for a long time.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between porosity and spalling resistance of Al ₂ O ₃ -based refractory materials and MgO-based refractory materials.

FIG. 2 is a diagram showing a configuration of a continuous casting immersion nozzle of the present invention.

FIG. 3 is a view showing a configuration of a conventional continuous casting immersion nozzle.

FIG. 4 is a diagram showing the relationship between the damage amount of the nozzle inner tube of the immersion nozzle and the casting time of the products 1 and 2 of the present invention obtained in Examples and the comparative product obtained in Comparative Examples.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C04B 38/00 303 C04B 35/10 F

Claims (4)

[Claims] 1. In a continuous casting immersion nozzle used for injecting molten steel from a tundish into a mold, a porous refractory material is used in a portion of the immersion nozzle which is in contact with molten steel. Immersion nozzle for continuous casting of contained steel. 2. The immersion nozzle for continuous casting of high oxygen content steel according to claim 1, wherein the porous refractory material is composed of oxide and / or non-oxide. 3. A porous refractory material having an apparent porosity of 20 to 6
The immersion nozzle for continuous casting of high oxygen content steel according to claim 1 or 2, which has 0% and an average pore diameter of 0.02 to 0.5 mm. 4. The immersion nozzle for continuous casting of high oxygen content steel according to claim 1, wherein the thickness of the porous refractory material is 2 to 10 mm.