JPH0662350B2 - Breathable refractory - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a breathable refractory used for gas bubbling in continuous casting of steel.

[Conventional technology]

At the junction of the tundish stopper and the upper nozzle in the continuous casting facility, and around the discharge hole such as the immersion nozzle,
A refractory material having spalling resistance and corrosion resistance is required.

As this refractory, alumina graphite or a zirconia graphite material described in Japanese Patent Publication No. 59-19067 is often used.

And the following method is adopted in order to give breathability to these refractories.

The first method is a method of making the structure porous by adjusting the particle size constitution of the refractory particles and imparting air permeability to the molded body, and the second method is to add and knead the organic fiber to the refractory raw material and mold it. After that, the organic fibers are burned off in the firing process to form voids to provide air permeability.

[Problems to be Solved by the Invention]

The above-mentioned carbon-containing refractory material obtained by the conventional preparation method and having air permeability has its respective drawbacks.

The first method by adjusting the particle size reduces the strength because the tissue itself is made porous, and when applied to a part such as a tundish stopper or upper nozzle to which external force is applied during use, the strength is insufficient. Breakage occurs, and breakage due to impact of molten steel flow becomes a problem at the discharge hole of the immersion nozzle.

The second method is more effective than the first method because it can reduce the decrease in strength, but it is inferior in wear resistance, and the bubbling of the inert gas stirs the molten steel to ablate the surface of the refractory. The loss is promoted and the service life is hindered.

In particular, when treating a molten steel in which non-metallic inclusions in the molten steel are likely to adhere and grow, as in the case of Al-killed steel, the wear erosion loss on the surface of the refractory material causes non-metallic inclusions around the discharge hole. It promotes adhesion and growth and hinders the gas bubbling function of the porous refractory, which is also a major factor that makes long-time casting operations impossible.

The problem to be solved in the present invention is, in a porous refractory used for such an application, the refractory itself has strength and wear resistance, and further, there is no adhesion to non-metallic inclusions and gas bubbling property. This is to provide a breathable refractory material that can maintain

[Means for Solving the Problems]

The present invention focuses on the fact that wear erosion due to molten steel flow of graphite-containing refractory in such applications is due to oxidation of carbon in the refractory and weakening of the structure due to melting of the carbon into molten steel. Has been completed.

Therefore, in order to maintain the gas bubbling function of the refractory and improve wear resistance, firstly, it is necessary to prevent oxidation of carbon in the refractory and secondly to prevent carbon from coming into contact with molten steel. The protection is effective.

As a concrete means for preventing carbon oxidation, metal powder such as silicon or aluminum having a function of capturing oxygen is added, and in order to prevent carbon from contacting molten steel, SiC, B Add carbide such as ₄ C,
It is considered that a glassy protective film is formed by heating at high temperature.

However, these means are accompanied by a densification phenomenon of the entire structure due to heating from the molten steel in use. Therefore, as a breathable refractory, it leads to a reduction in breathability, and is unsuitable as a refractory for stable bubbling.

The present invention utilizes the fact that a refractory raw material (ZRM raw material) whose main mineral phase is mullite, badderite, or corundum can be most suitably used for such purpose.

That is, the breathable refractory material of the present invention comprises mullite, badderite, and corundum as the main mineral phases, and Al ₂ O
₃ Refractory raw material with chemical composition of 25-85% by weight, ZrO ₂ 10-70% by weight, SiO ₂ 5-25% by weight, and 30-60% by weight and graphite powder 10
-30% by weight, and after adding and kneading the organic fibers thereto, the organic fibers are burnt out in the firing process to form voids to impart air permeability.

Figure 1 shows the load softening characteristics of a refractory made of two types of ZRM materials. As is clear from the figure, softening due to vitrification begins near 1550 ° C, which is close to the temperature of molten steel, in all cases. Is shown.

Therefore, when using ZRM raw material for breathable refractory,
Vitrification occurs only in the surface layer in contact with molten steel. On the other hand, the formation of glass does not occur inside the refractory material having a relatively low temperature. This makes it possible to prevent the oxidation of carbon required for the above-mentioned applications, the effect of protecting from molten steel, and the prevention of densification of the entire structure.

As ZRM raw material, ZrO ₂ 10 to 70 wt%, Al ₂ O ₃ 25 to 85
Those having a chemical composition of wt% and SiO ₂ 5 to 25 wt% can be preferably used.

However, when ZrO ₂ is less than 10% by weight, the softening point (T ₁ ) is 16
If the temperature exceeds 00 ° C., a glassy composition is difficult to form, and if it exceeds 70% by weight, abnormal expansion peculiar to ZrO ₂ is exhibited and spalling resistance is deteriorated, which is not preferable.

Further, the amount of graphite added is preferably within the range of 10 to 30% by weight from the viewpoints of the separability (wetting resistance) of the refractory itself to molten steel and slag, the oxidation resistance, and the strength.

Further, as the organic fiber, a polyester having a melting point of 1000 ° C. or lower, which is burnt off by firing,
Materials such as Tetron and nylon are preferable. From the viewpoint of imparting air permeability and maintaining strength, the amount of addition is preferably adjusted to the range of 0.2 to 2% by weight. The length of organic fiber is 1
It is preferably 30 mm or less in terms of the effect of providing air permeability and the prevention of fiber aggregation during mixing. Furthermore, its diameter is 30
It is preferably in the range of from 200 to 200 μm in terms of prevention of fiber breakage and easy adjustment of pore diameter. Especially 200
If it exceeds μm, the pore diameter becomes too large and molten steel will enter.

〔Example〕

After kneading each composition shown in Table 1, use a rubber press at a pressure of 1200 kg / cm ² to mold an inner cylinder of outer diameter 300 × inner diameter 130 × length 70 (mm) in a non-oxidizing atmosphere at 1000 ° C. It was calcined and the quality was measured.

In addition, the following various breathable refractories were used at the tip of the long stopper for practical use.

In Table 1, Examples 1 and 2 are within the scope of the present invention.

In the breathability tests of Examples 1 and 2, even after heating by immersion in molten iron, the same breathability as that before heating was maintained and stable breathability was exhibited. In addition, as a result of actual furnace test using the tip of the long stopper, it showed good wear resistance and corrosion resistance.
Withstood the use of charges.

In Comparative Examples 1 and 2, the ZRM amount is less than the range of the product of the present invention,
In addition, it does not contain metal powders such as silicon and aluminum and carbides such as SiC and B ₄ C which are oxidation resistant raw materials. In the air permeability test in this case, there is no change in the air permeability after the molten iron is heated, but as a result of the actual furnace test using the tip of the long stopper, the tip was severely worn and discarded after 5 times of charging. It was

In Comparative Example 3, the amount of ZRM used was larger than the range of the product of the present invention, and no oxidation resistant raw material such as silicon, aluminum, SiC, B ₄ C was contained.

In this case, the erosion test showed a large amount of melting loss, and the actual furnace test showed a large amount of melting loss.

Comparative Examples 4 and 5 do not use ZRM but use an oxidation resistant raw material. In the air permeability test in this case, the air permeability after heating by immersion in molten iron is reduced to less than 1/2 and there is a problem in stability of air permeability.

FIG. 2 shows specific application points of the refractory material of the present invention.

In the figure, the breathable refractory of the present invention is a site where non-metallic inclusions in steel adhere and grow to cause blockage, that is, the tip part 1b of the tundish stopper and the head part 2b of the upper nozzle to be joined thereto. It was applied to the discharge hole portion 3b of the immersion nozzle.

When these breathable refractories were used for casting aluminum killed steel, they could withstand continuous use for 500 minutes (In the conventional casting without bubbling, non-metallic inclusions clogged up in 300 minutes and the casting was stopped. ).

By bubbling the inert gas from the 1b, 2b, and 3b parts, stable bubbling can be performed without changing the air permeability during casting.
It was possible to prevent non-metallic inclusions from adhering to these parts, and almost no wear or melting damage was observed at the tip.

[Effects of the Invention] The effects of the refractory material according to the present invention are summarized as follows.

(1) Since there are few variations in strength and breathability, and excellent spalling resistance, problems such as breakage and cracking due to spalling do not occur at all, especially as a breathable refractory for continuous casting gas bubbling of steel. It can be used stably.

(2) Since there is almost no decrease in the air permeability due to heating, stable bubbling is possible even during long-term casting, and adhesion of non-metallic inclusions can be prevented.

(3) By forming a glass film on the surface layer that comes into contact with molten steel, it is possible to prevent oxidation of carbon and leaching into the molten steel, resulting in reduced melting loss and wear and withstanding long-term use. You can

[Brief description of drawings]

FIG. 1 is a diagram showing the characteristics of the ZRM raw material used in the present invention, and FIG. 2 is a diagram showing an application example of the refractory material of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Nakamura 1 Kimitsu, Kimitsu-shi, Chiba Shin Nippon Steel Co., Ltd. Inside the Kimitsu Steel Works, Kaisha (72) Noboru Okuyama 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Stocks Incorporated by Kimitsu Works (56) References JP-A 61-97161 (JP, A) JP-A 60-112680 (JP, A)

Claims (1)

[Claims] 1. A main mineral phase consisting of mullite, badderite, and corundum. Al ₂ O ₃ 25-85 wt%, ZrO ₂ 10
~ 60 wt%, SiO ₂ 5 ~ 25 wt% of a refractory raw material having a chemical composition of 30 ~ 60 wt% and graphite powder 10 ~ 30 wt%, after adding organic fibers to this and kneading and molding A breathable refractory material, characterized in that the organic fibers are burned out in the firing process to form voids to provide breathability.