JPH05360A - Immersion nozzle for continuous casting - Google Patents

Abstract

(57) [Summary] [Object] To provide a continuous casting immersion nozzle capable of stably casting stainless steel for a long time. [Constitution] The main component is composed of 15 to 35% by weight of graphite, 20 to 60% by weight of β-alumina having a maximum particle size of 1 mm or less, and 25 to 65% by weight of α-alumina of maximum particle size of 74 μm or less. It is characterized in that Si, SiC, and SiO ₂ are not separately added, except for glass components as unavoidable impurities contained in ash and β-type alumina and α-type alumina. [Effect] Especially when casting stainless steel, it is possible to prevent infiltration and melting damage of the metal in the nozzle inner hole portion, and it can be used stably for a long time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dipping nozzle for continuous casting of steel, and particularly when casting stainless steel, prevents invasion and melting damage of the metal in the nozzle inner hole and ensures stable and long-term operation. The present invention relates to a continuous casting immersion nozzle that can be cast.

[0002]

As a refractory for continuous casting used to inject molten steel from a tundish into a mold, Al ₂ O ₃ --SiO ₂ --graphite refractory is generally used.
In particular, since stainless steel has a relatively high oxygen level in the steel, the rate of SiO ₂ in the refractory material limits the rate of infiltration and melting of the metal in the nozzle bore, and it can only be used for a short time. . For this reason, Al ₂ O ₃ —SiC—graphite refractory from which SiO ₂ component in the refractory is removed is being used for casting of stainless steel. However, in the case of casting for a long time (for example, 500 min or more), the infiltration and melting loss of the metal into the nozzle inner hole portion may occur due to the progress of the oxidation reaction of SiC in the refractory and the subsequent reduction reaction, as described above. Since it progresses, stable casting cannot be achieved over a long period of time.

[0003]

With regard to continuous casting of stainless steel having a relatively high oxygen level and a low viscosity in the steel, Al ₂ O ₃ --SiO ₂ --graphite refractory, which is one of the prior arts, is used. In the working part of the nozzle hole where the temperature drops drastically, the metal oxides generated such as FeO, MnO, etc. accompanying the precipitation of oxygen in the steel selectively react with SiO ₂ in the refractory material to melt, flow away and melt damage. Will progress. Further, since SiO ₂ is considerably unstable in a reducing atmosphere at a high temperature, it is gasified by the reduction reaction with C in the refractory and the structure becomes brittle. In addition, FeO and MnO produced in the working part of the nozzle inner hole
And Cr ₂ O _{3 and the} like are reduced by C in the refractory, the consumption of C progresses, and the embrittlement of the structure further progresses. By repeating the above-mentioned reaction, infiltration and melting loss of the metal were sequentially generated, and finally a trouble such as abnormal melting loss or falling out was reached, and it was possible to withstand only about 200 minutes.

Therefore, in order to further extend the service life, SiO
_In some cases, Al ₂ O ₃ —SiC—graphite refractory without adding ₂ may be used as a countermeasure. It is possible to extend the life stably up to about 500 min, but 500 min
It cannot be used stably for the above-mentioned use, and infiltration of the metal is likely to occur especially around the discharge hole where static pressure is applied. Since there is almost no hot strength in the infiltrated layer, in the worst case, the ejection holes fall.

After all, this is considered to be caused by SiC in the refractory, and the oxidation of SiC due to a time factor causes the formation of an infiltrated layer of the bare metal in the same manner as described above. It lacks stability in time casting.

Next, other characteristics will be described. Low expansion Al ₂ SiO ₂ is not contained as a raw material of the O ₃ - For the graphite-based refractory, using only α-type for Al ₂ O ₃ Al ₂ O ₃ raw material, the high thermal expansion properties of the α-type alumina The thermal spalling characteristics due to the above tend to be greatly deteriorated.

Therefore, an object of the present invention is to prevent sudden occurrence of a metal infiltration layer in the nozzle inner hole portion even when it is used for casting stainless steel for a long time of 500 min or more, and it is sudden. Provided is a continuous casting nozzle capable of stable casting without causing a large thermal spalling.

[0008]

The present invention has been made in order to solve the above-mentioned problems, and it is an immersion nozzle for continuous casting other than a portion B corresponding to the slag line of the immersion nozzle 1 of FIG. use. That is, as a main component in part A of FIG. 1, graphite is 15 to 35% by weight, β-alumina having a maximum particle size of 1 mm or less is 20 to 60% by weight, and the maximum particle size is 74 μ.
α-alumina of m or less, composed of 25 to 65% by weight,
Except for the ash content of graphite and the glass-based components as unavoidable impurities contained in β-type alumina and α-type alumina,
This is a continuous casting immersion nozzle in which an alumina-graphite refractory is arranged, in which Si, SiC, and SiO ₂ are not added separately.

[0009]

According to the present invention, as the main component of the alumina-graphite refractory in the immersion nozzle for continuous casting of stainless steel,
The graphite content is preferably 15 to 35% by weight. When the content is less than 15% by weight, the thermal conductivity is lowered and the thermal expansion coefficient is increased, so that the heat resistant spalling property is deteriorated, and when the content exceeds 35% by weight, the oxidation resistance and the corrosion resistance are deteriorated. Will be drastically reduced.

The content of β-alumina is preferably 20 to 60% by weight. β-alumina has a chemical composition of 11A
It is represented by l ₂ O ₃ · R ₂ O (R = Na, K), and its crystal structure is a hexagonal system like α-type alumina, but the lattice constant of the crystal is different and it is perpendicular to the crystal axis. Since it has a remarkable easiness of use in the direction and the particles are on a flat plate having elasticity, the heat-resistant spalling property can be improved more than that of α-alumina, but when it exceeds 60% by weight, R _{2 in the} crystal is increased. O
The oxidation of graphite is promoted by the influence of (R = Na, K) component, and R is exposed when exposed to high temperature and reducing atmosphere for a long time.
Due to the vaporization of the ₂ O (R = Na, K) component, β-type alumina collapses and corrosion resistance decreases. If it is less than 20% by weight, the heat-resistant spalling property cannot be maintained at a high level.

The particle size of β-type alumina is 1 m as the maximum particle size.
A value of m or less is suitable, and if it is more than m, the mixing property with other raw materials deteriorates, causing variations in physical property values, and showing a low strength. The content of α-alumina is preferably 25 to 65% by weight. That is, the content is 25
If it is less than wt%, the corrosion resistance will be deteriorated, and if it exceeds 65 wt%, the heat-resistant spalling property will be greatly deteriorated. The maximum particle size of α-alumina is appropriately 74 μm or less, and if it is larger than that, the corrosion resistance cannot be expected to be improved and the strength will be low.

Next, the continuous casting immersion nozzle of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic vertical section of a continuous casting immersion nozzle according to the present invention. By arranging the refractory material having the chemical composition of the present invention in the portion A of the immersion nozzle 1 of FIG. 1, when casting stainless steel, the metal ingot will come out from the nozzle inner hole that is in contact with molten steel for a long time. It can be used stably without infiltration.

[0014]

The effects of the present invention will be described below with reference to examples.

[0015]

EXAMPLES Formulations 1 to 6 (hereinafter referred to as “samples of the invention”) having chemical composition within the scope of the present invention shown in Table 1 and formulations 7 to having chemical composition outside the scope of the present invention 5 to 1 for each of 9 (hereinafter referred to as "comparative sample")
Oxygen concentration was 100 ppm and Mn concentration was 1.0-1.Mn based on the raw material kneaded material obtained by adding powder and solution phenol resin in the range of 0 wt% and mixing and kneading them.
5%, molded body having dimensions of 30 mm × 30 mm × 230 mm for testing corrosion resistance to molten steel adjusted to 1550 ° C. and outer diameter 150 mm, inner diameter 60 mm and total length 400 for testing spalling resistance
A molded body having a size of mm is produced and each of
Refractory 1 to 1 by reduction firing at a temperature in the range of 1200 ° C
1 was produced.

Table 1 shows the physical endurance values of the above-mentioned samples 1 to 6 of the present invention and comparative samples 7 to 11.

Next, the above-mentioned 30 mm × 30 mm × 23
Each of Samples 1 to 6 of the present invention and Comparative Samples 7 to 11 having a dimension of 0 mm had an oxygen concentration of 100 p.
1550 with pm and Mn concentrations adjusted to 1.0 to 1.5%
The melting loss rate was investigated by immersing in molten steel at a temperature of ° C for 180 minutes, and the results are shown in Table 1.

Then, the above-mentioned outer diameter 150 mm and inner diameter 60
155 for each of Samples 1-6 of the present invention and Comparative Samples 7-11 having dimensions of mm and total length of 400 mm.
After being immersed in molten steel at 0 ° C. for 10 minutes, it was quenched from the outer surface with water, the presence or absence of cracks was confirmed, and the spalling resistance was investigated. The results are shown in Table 1.

As is clear from Table 1, the sample of the present invention has excellent spalling resistance and corrosion resistance, while the comparative sample, for example, sample 7, has a low graphite content, and The result was that the spalling resistance was significantly inferior due to the high content of α-alumina. Further, in Comparative Sample 8, the corrosion resistance is remarkably poor due to the high graphite content, and in Comparative Sample 9, the comparative sample 9 is low in the α-alumina content. In 10 and 11, the chemical composition value is
Although it is the same as the sample 2 of the present invention, the strength was low and the melt loss rate was deteriorated due to the coarse particle size of β-type and α-type alumina.

On the basis of the above results, in the sample 2 of the present invention shown in Table 1, the immersion nozzle for continuous casting shown in FIG. 1 was prepared, and a ladle 70 ton stainless steel (JIS standard: SUS304) slab series was prepared. When it was set in a casting machine and cast for 900 minutes with an actual machine, no infiltration of the metal in the nozzle inner hole was observed and it was proved that it could be used stably for a long time.

From these results, the immersion nozzle using the alumina-graphite refractory having the chemical composition of the present invention makes it possible to cast stainless steel for a long time.

[Brief description of drawings]

FIG. 1 is an explanatory longitudinal sectional view of a continuous casting immersion nozzle of the present invention.

[Explanation of symbols]

1 immersion nozzle Part A B part

Claims (3)

[Claims] 1. A dipping nozzle for continuous casting of alumina-graphite, containing 15 to 35% by weight of graphite, 20 to 60% by weight of β-type alumina, and 25 to 65% by weight of α-type alumina as main components. Immersion nozzle for continuous casting characterized by 2. Alumina-graphite refractory contains Si, SiC, SiO ₂ except for graphite ash and glass-based components as unavoidable impurities in β-type alumina and α-type alumina.
2. The immersion nozzle for continuous casting according to claim 1, wherein is not added separately. 3. The continuous casting immersion nozzle according to claim 1, wherein the maximum particle size of β-alumina is 1 mm or less and the maximum particle size of α-alumina is 74 μm or less.