JPH09255407A - Carbon-containing refractory and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carbon-contg. refractory suppressed in thermal shock resistance decline without deteriorating both the corrosion resistance and oxidation resistance inherent therein. SOLUTION: This carbon-contg. refractory is such one that there are plural cracks in each of aggregate granules each >=1mm in size as a constituent and the graphite as the carbon matrix has no crack. This refractory is obtained by molding through striking the original refractory by use of a friction press under normal or reduced pressure, and even after the molding density reaches a maximum, further continuously striking it to develop cracks in the aggregate granules. The intensity of the striking is set at >=0.5t/cm<2> in terms of pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon-containing refractory used as a refractory for an inner wall of a converter, a hot metal car, etc., and a method for producing the same.

[0002]

2. Description of the Related Art A refractory used as a lining material for a molten metal refining vessel is required to have excellent slag erosion resistance, thermal shock resistance, and abrasion resistance. In most cases, refractory materials containing carbon-containing refractory aggregate as a main component are the mainstream. For example, a magnesia-carbonaceous refractory is used as a lining material for a converter. However, as the refining temperature and secondary combustion ratio have risen with the recent upgrading of steel, and as seen in the new smelting reduction method and scrap melting method, the conditions under which bricks are used have become extremely severe. . On the other hand, an alumina-silicon carbide-carbon refractory material is widely used as a lining material for a hot metal car. However, as can be seen from the recent increase in the hot metal pretreatment ratio due to gas acid, the conditions for using bricks are also extremely severe in this case.

[0003]

The role of carbon in such a carbon-containing refractory is to improve the corrosion resistance to slag by utilizing the property of carbon that is poorly wettable by slag, and to improve the low elasticity and high thermal conductivity of carbon. There are two ways to improve the thermal shock resistance used. For example,
In the case of a magnesia-carbonaceous refractory for a converter, a carbon amount of 5% by weight or more is sufficient from the viewpoint of improving the corrosion resistance against slag. However, from the viewpoint of ensuring thermal shock resistance, it is required to be 10% by weight or more. Therefore, in order to satisfy both characteristics, a carbon content of 10% by weight or more is generally used.

On the other hand, for the purpose of suppressing the oxidation of carbon, conventionally, metal, carbide, and
A method of adding a boride or the like has been proposed. For example,
For magnesia-carbonaceous refractories, Japanese Patent Publication Sho 60
-163393, Al, JP-A-60-200857.
It is disclosed in Japanese Patent Publication No. JP-A-2003-242121 to add a low melting point alloy.

However, the addition of these oxidation inhibitors has the adverse effect of reducing the thermal shock resistance. For example,
In order to use the magnesia-carbon refractory in a strong oxidizing atmosphere, it is necessary to add a large amount of metal such as Al and Si, and as a result, the elastic modulus of the refractory is improved and the thermal shock resistance is lowered. Invite.

It is an object of the present invention to provide a refractory material containing carbon, in which the thermal shock resistance is suppressed from being lowered without lowering the corrosion resistance and the oxidation resistance of the refractory material itself. is there.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been earnestly studied in view of the above-mentioned problems of the prior art. As a result, the carbon-containing refractory bones are formed in the molding step performed after the raw materials are blended and kneaded. The inventors have found that the problem can be solved by generating cracks in the material particles, and completed the present invention.

That is, the present invention is a carbon-containing refractory having a plurality of cracks in the aggregate particles having a particle diameter of 1 mm or more and constituting the refractory, and having no cracks in the graphite of the carbon matrix, The manufacturing method is that when a carbon-containing refractory is molded by hitting it using a friction press under normal pressure or reduced pressure, even after the molding density reaches the maximum, the carbon-containing refractory is further continued. It is characterized in that a crack is generated in the aggregate particles by hitting. At this time, the strength of the impact applied when molding using a friction press is converted to a pressure of 0.5 t.
/ Cm ² or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The aggregate particles of the carbon-containing refractory used in the present invention are metal oxides such as alumina, magnesia, and zirconia. As a raw material for these aggregate particles, those having a large crystallite size and high purity are preferable from the viewpoint of maintaining corrosion resistance. For example, in the case of a magnesia-carbonaceous refractory, a crystallite diameter of 100 μm or more and B ₂ O ₃ as a raw material of magnesia
A high-purity product with a low content of 96% or more is sintered or electrofused, or seawater magnesite or natural magnesite is electrofused.

As the carbon powder mainly composed of graphite, carbon raw materials such as coke, carbon black, and mesophase carbon can be used in addition to natural or artificial graphite. Is preferred.

Using these magnesia raw materials and carbon powder, an appropriate amount of organic binder such as pitch, tar, phenolic resin, modified phenolic resin or silicon resin is added to the magnesia-graphite compounded raw material composition and mixed. Using a friction press under normal pressure or reduced pressure, a pressure of 0.5 t / cm ² or more in terms of pressure is molded.

FIG. 1 shows the relationship between the number of hits and the molding density of a molded body when molded using a friction press under reduced pressure. In the conventional molding method, the molding is completed when the molding density reaches the maximum, but in the present invention, the carbon-containing refractory is continuously hit and molded even after the molding density reaches the maximum.

In the aggregate particles of the carbon-containing refractory material obtained by such a method, as shown in FIG.
Multiple cracks occur due to impact force during molding. As a result, the elastic modulus of the refractory material is lowered, and the thermal stress caused by the cracks generated during actual operation can be relieved to improve the thermal shock resistance. On the other hand, the graphite of the carbon matrix in the carbon-containing refractory is more likely to be plastically deformed than the aggregate particles, so that even if an impact force is applied at the time of molding, mechanical stress caused by the impact force can be relaxed. like,
It becomes a crack-free carbon matrix. Therefore, the carbon-containing refractory does not show any adverse effects on the quality such as a decrease in mechanical strength and the occurrence of internal defects. On the contrary,
In the case of a carbon-containing refractory obtained by a conventional manufacturing method,
As shown in FIG. 3, neither aggregate particles nor carbon matrix shows cracks.

Here, the strength of impact is 0.
When it is less than 5 t / cm ² , a plurality of cracks are hardly generated in the aggregate particles, and therefore, the elastic modulus of the obtained refractory hardly decreases. As a result, the thermal shock resistance is not improved and is not suitable for the present invention.

For molding the carbon-containing refractory, there is an oil press in addition to the friction press under normal pressure or reduced pressure used in the present invention. However, in the oil press, since the pressing pattern requires a few seconds, and since the impact force is not directly applied to the carbon-containing refractory, cracks do not occur in the aggregate particles of the carbon-containing refractory, so that the present invention is not required. Not suitable. For the definition of the friction press used in the present invention, refer to 219 of “Developing Refractory Engineering” (published on the first print on August 20, 1987) edited by Refractory Technology Association.
Pp. 224.

[0016]

EXAMPLES The present invention will be described in more detail below with reference to examples. An example is a magnesia-carbonaceous refractory used as a lining material for a converter. That is, as a magnesia source, a purity of 9 from seawater magnesite was used.
After adding 90 parts by weight of 9.5% magnesia, 10 parts by weight of natural scaly graphite having a purity of 98%, and further adding 3 parts by weight of Al having a purity of 99% as an oxidation inhibitor, and mixing them,
3 parts by weight of a phenolic binder was added and kneaded.

The kneaded material obtained had a molding surface of 1000 mm ×
It is put in a mold that can obtain a molded body having a thickness of 150 mm and a thickness of 150 mm, and converted into pressure of 0.3 t / cm ² , 0.5 t / c.
Three levels of m ² and 0.7 t / cm ² were formed by applying 7 hits with a friction press to form a brick having a bulk specific gravity of 2.80. This was used as a comparative material, and apart from this, a material subjected to friction press molding by being hit 14 times was prepared. After heat-treating the thus obtained brick in a nitrogen atmosphere at 250 ° C. for 24 hours,
It was used as a test sample.

First, the method for evaluating the bricks after the heat treatment will be described below. The bulk specific gravity was determined by the Archimedes method. Also, 40 × 40 × 23 for measuring mechanical strength
A test piece cut into a size of 0 mm was prepared, and the dynamic elastic modulus was measured by an ultrasonic method, and the compression strength was measured by a compression test.

As for the oxidation resistance, a magnesia-carbonaceous refractory test piece cut out into a certain shape (here, the same as the above-mentioned test piece for measuring mechanical strength) was subjected to 5 ° C. in an air atmosphere.
After heating up to 1400 ° C. at a heating rate of / min, the temperature was maintained for 3 hours, the central portion of the test piece was cut, and the thickness of the decarburized layer was measured and evaluated. The larger the decarburization index obtained by indexing the thickness of the decarburized layer, the poorer the oxidation resistance.

The corrosion resistance was evaluated by lining a test piece cut out in a certain shape (same as above) in a high frequency induction furnace, measuring the thickness of the maximum wear portion, and indexing this thickness. At that time, electrolytic iron was used as the steel to be charged into the furnace, and the slag having a composition of CaO / SiO ₂ = 3.5 and FeO = 22% by weight was heated to a molten steel temperature of 1680 ° C. Held for 5 hours.

Regarding the thermal shock resistance, a test piece cut into a certain shape (same as above) was immersed in hot metal at 1600 ° C. for 90 seconds, and then allowed to cool in a room temperature atmosphere for 3 minutes, which was repeated 20 times. Investigate the number of times it occurs until it comes off,
This number of times was evaluated. The greater the number of times that peeling occurs, the better the thermal shock resistance.

Table 1 shows examples and comparative examples of the present invention. In addition, the results of molding at the above-mentioned three levels of molding pressure using an oil press are also shown.

[0023]

[Table 1]

As shown in Comparative Examples 1, 2 and 3, a molded body could not be obtained by the oil press. Also,
As shown in Comparative Example 7, when the molding pressure of the friction press is 0.3 t / cm ² , the dynamic elastic modulus does not decrease and the thermal shock resistance is not improved. On the other hand, as shown in Examples 1 and 2, the molding pressure was 0.5 t / cm ² or more, and Comparative Example 5
And 6 times, a plurality of cracks are generated in the magnesia particles that are aggregates, and the dynamic elastic modulus is lowered. As a result, the thermal shock resistance could be significantly improved.

[0025]

INDUSTRIAL APPLICABILITY The carbon-containing refractory material of the present invention has a plurality of cracks in the aggregate particles and is excellent in thermal shock resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the number of hits by a friction press under reduced pressure and the molding density when molding a magnesia-graphite refractory material.

FIG. 2 is a schematic diagram of the structure of a carbon-containing refractory material of the present invention.

FIG. 3 is a schematic diagram of the structure of a conventional carbon-containing refractory material.

[Explanation of symbols]

 1 carbon matrix 2 cracks 3 aggregate particles

Claims (3)

[Claims] 1. A carbon-containing refractory having a plurality of cracks in the aggregate particles having a particle diameter of 1 mm or more and constituting the refractory, and having no cracks in the graphite of the carbon matrix. 2. When the carbon-containing refractory is molded by hitting with a friction press under normal pressure or reduced pressure, even after the molding density reaches the maximum, the carbon-containing refractory is further continued. A method for producing a carbon-containing refractory material, characterized in that a crack is generated in the aggregate particles by hitting. 3. The method for producing a carbon-containing refractory material according to claim 2, wherein the impact strength applied when molding using a friction press is converted into a pressure of 0.5 t / cm.
^A method for producing a carbon-containing refractory material, characterized in that the number is ² or more.