JPH07277838A - Production of nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To provide a nozzle for continuous casting such excellent heat and impact resistance that fractures are not generated even under severe use conditions, such as rapid heating and quenching by forming and sintering a material mixed with an organic solvent solution of reformed pitch to a compound consisting essentially of fire resistant oxide and carbon material. CONSTITUTION:The nozzle for continuous casting is produced by adding a solution in which 2-4wt.% of reformed pitch is dissolved in an organic solvent to 100wt.% of a composition consisting essentially of fire resistant oxide and carbon material before mixing them and forming and drying the mixture before sintering it. As the reformed pitch, that which is soluble in an organic solvent and has a crystalline phase or a mixed phase of the crystalline phase and an amorphous phase and whose weight reducing rate is <=30% when it is sintered at it is sintered at 800 deg.C in a nonoxidizing atmosphere is preferably used. As the organic solvent, an aromatic compound or a heterocyclic compound is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a nozzle for continuous casting used in the steel industry.

[0002]

2. Description of the Related Art A nozzle for continuous casting is an important member used for pouring molten metal from a ladle into a tundish or casting from a tundish into a mold in the continuous casting process of steel. Is. By using this nozzle, oxidation of molten metal, inclusion of non-metallic inclusions,
Alternatively, turbulent flow splash and the like can be prevented. On the other hand, since the continuous casting nozzle is used under extremely severe conditions, it is required to have particularly excellent thermal shock resistance, corrosion resistance and mechanical strength.

Conventionally, siliceous materials have been used for continuous casting nozzles. However, recently, mainly using a phenolic resin as a binder, a carbon-bonded alumina-graphitic (AG) material, zirconia-
Graphite (ZG) materials and the like are used (for example, JP-A-57-3258). The nozzle for continuous casting using this AG material or ZG material exhibits high strength because it has a carbon bond inside its structure, is excellent in thermal conductivity and thermal shock resistance, and is also excellent in corrosion resistance. There is.

On the other hand, as a binder for forming a carbon bond, a phenol resin is generally used, but for the purpose of further improving the strength, mesophase pitch (with a pitch molecule having regularity among modified pitches) is used. Those which are oriented and have an optically anisotropic structure are also used (for example, JP-A-5-4861 and JP-A-5-2708).
No. 89).

[0005]

However, there is a drawback in that carbon forming a carbon bond is oxidized or decarburized in an oxidizing atmosphere at a high temperature and the strength is remarkably lowered. Moreover, the thermal shock resistance is not sufficient under severe operating conditions such as rapid heating and rapid cooling. For example, a large number of cracks are generated on the inner surface or the surface of the continuous casting nozzle that is rapidly heated by contacting with high temperature molten steel, and the generated cracks propagate and expand to form the continuous casting nozzle. It is often observed that refractories come off. As a result, there is a problem that entrainment of oxygen occurs and the quality of the obtained steel deteriorates.

An object of the present invention is to provide a method for producing a continuous casting nozzle having excellent thermal shock resistance, which does not cause cracks even under severe use conditions such as rapid heating and rapid cooling.

[0007]

In order to improve thermal shock resistance, a method for manufacturing a continuous casting nozzle according to the present invention comprises:
After adding a solution in which 2 to 4% by weight of modified pitch is dissolved in an organic solvent to a compound 100 containing a refractory oxide and a carbon material as main components, they are mixed and molded and dried. ,
It is characterized by firing. Alternatively, to the compound 100 containing a refractory oxide and a carbon material as main components, and Al or Si powder added thereto, a solution prepared by dissolving 2 to 4% by weight of modified pitch in an organic solvent was added. After that, the strength is further improved by mixing, molding, drying and firing the mixture.

In these methods, the modified pitch is soluble in an organic solvent and has a crystalline phase or a mixed phase composed of a crystalline phase and an amorphous phase, and is 800 in a non-oxidizing atmosphere. A material having a weight loss rate of 30% or less when fired at ℃ is used. Further, as the organic solvent, an organic solvent or an aromatic compound is added in an amount of 2 to 10% by volume with respect to 100% by volume of the mixture. The raw materials thus obtained are mixed, molded and dried, and then 1200
Firing is performed within the range of ˜1400 ° C.

[0009]

The nozzle for continuous casting of the present invention comprises a slab continuous casting machine, a bloom continuous casting machine, a billet continuous casting machine, a twin roll type continuous casting machine, a twin belt type continuous casting machine, a single belt type continuous casting machine, and a single roll type. Long nozzles and immersion nozzles used in continuous casting machines. In the production of the nozzle for continuous casting according to the present invention, natural or artificial graphite, mesophase carbon, coke, carbon black or the like is used as a carbon material, and a carbon material having a purity of 90% or more is used to prevent deterioration of corrosion resistance due to impurities. desirable.

The refractory oxides are neutral or acidic refractory oxides which have excellent corrosion resistance and are difficult to react with carbon, such as fused alumina, sintered alumina, fused zirconia, sintered zirconia, and fused alumina. Calcium zirconate or the like can be used, and the purity is preferably 90% or more in order to prevent deterioration of corrosion resistance due to impurities.

FIG. 1 shows the modified sample of fused pitch (80% by weight) and scaly graphite (20% by weight) dissolved in quinoline, added, molded and fired. It shows the relationship between the amount of fine pitch added and the bending strength.

The modified pitch is added in an amount of 2 to 4% by weight based on 100 of the composition containing the refractory oxide and the carbon material as main components.
The reason is that the hot strength and thermal shock resistance are excellent, based on the results of the experiment conducted by the present inventors using fused alumina and scaly graphite shown in FIG. The amount of modified pitch added is 2
If it is less than 4% by weight or more than 4% by weight, hot strength and thermal shock resistance are deteriorated, which is not preferable.

The amount of organic solvent added is 100% by volume of the blend.
On the other hand, the reason why the amount is 2 to 10% by volume is that the dispersibility of the modified pitch at the time of kneading and the filling property at the time of molding are excellent at this addition amount. If the added amount of the organic solvent is less than 2% by volume, the dispersibility at the time of kneading and the filling property at the time of molding are poor, and if it exceeds 10% by volume, the molding becomes impossible, which is not preferable.

The modified pitch used in the present invention is soluble in an organic solvent, has a crystalline phase or a mixed phase consisting of a crystalline phase and an amorphous phase, and is 800 ° C. in a non-oxidizing atmosphere.
It is desirable that the weight loss rate is 30% or less when the firing is performed at.

Further, the crystalline content in the modified pitch is 60.
% Or more is desirable. When the crystalline content in the modified pitch is less than 60%, the strength is low even if the modified pitch is added as a binder. Also, the modified pitch is set to 80
If the weight loss rate when fired at 0 ° C exceeds 30%,
It is not preferable because the hot strength is poor.

The organic solvent used in the present invention is an aromatic compound or a heterocyclic compound capable of dissolving the modified pitch, and specifically includes toluene, xylene, styrene, quinoline, pyridine, benzene and the like. The modified pitch used in the present invention has the following behavior during firing,
Thermal shock resistance is improved.

When the modified pitch is heated, it becomes a carbonized product having a graphite-like structure with a highly developed carbon hexagonal mesh plane, forming a strong carbon bond. In addition, the weight loss due to thermal decomposition is very small compared to phenolic resin and ordinary pitch. Therefore, when the modified pitch is used as the binder of the carbon-containing refractory material, the strength reduction due to thermal decomposition is suppressed, and conversely the hot strength is improved. Furthermore, by dissolving the modified pitch in an organic solvent and adding it to the refractory material, it becomes possible to uniformly disperse the modified pitch and to strengthen the entire refractory structure.

The carbonized material obtained from the modified pitch has a graphite-like structure and therefore has a higher thermal conductivity and a lower elastic modulus than the carbonized material obtained from the phenol resin. . By using such a modified pitch as a binder of a refractory material forming a nozzle for continuous casting, thermal stress generated by thermal shock is reduced, and thermal shock resistance can be improved.

In order to further improve the strength of the refractory material constituting the continuous casting nozzle of the present invention, Al or Si powder that reacts inside the refractory material to form a carbide, nitride or oxide during use. It is also possible to add.

FIG. 2 shows that fused alumina and scaly graphite are used.
It is the figure which showed the relationship between the amount of metal addition and bending strength about the sample after adding the powder of metal Al and Si, shaping and baking.

According to the results of experiments conducted by the present inventors using fused alumina and scaly graphite, as shown in FIG.
Alternatively, the strength increases with the addition amount of Si metal powder up to 10% by weight, but the strength decreases with the addition amount exceeding 10% by weight. Therefore, the addition amount of metal Al or Si is 10% by weight. The following is sufficient. Al or S
Also in the continuous casting nozzle of the present invention to which the powder of i is added, the effect of the modified pitch acts in the same manner as in the case where the above-mentioned addition is not made, and the thermal shock resistance can be improved.

In the present invention, a refractory oxide and a carbon material satisfying the above conditions are contained as main components, and if necessary, A
1 or Si powder was added, and to the compound 100 further containing unavoidable impurities, a solution prepared by dissolving 2 to 4% by weight of modified pitch in an organic solvent was added, and then mixed.
After it is molded and dried, it is subjected to reduction firing or firing in an inert gas atmosphere.

The firing temperature is 1200 ° C. or higher and 1400 ° C. or lower. When the firing temperature is less than 1200 ° C., the strength of the obtained nozzle is insufficient and the effect of the present invention cannot be obtained.
If the temperature exceeds 1400 ° C, the refractory oxide is reduced by the carbon material and the structure deteriorates, which is not preferable.

[0024]

EXAMPLES The present invention will be described below based on examples.

Example 1 An example in which toluene as an aromatic compound and quinoline as a heterocyclic compound are used as the organic solvent and the continuous casting nozzle obtained by the production method of the present invention is used is shown. Raw material composition 10 shown in Table 1
After adding modified pitch dissolved in an organic solvent as a binder to 0% by weight, kneading, rubber press molding, drying (90 ° C x 24 hours), reduction firing (1300 ° C)
X 3 hours) to produce the nozzle for continuous casting of the present invention.

[0026]

[Table 1A]

[0027]

[Table 1B]

Here, as the refractory oxide, fused graphite, sintered alumina, fused zirconia, sintered zirconia, and fused calcium zirconate are used as carbon materials, and scaly graphite having a purity of 99% is used. Si was used. The thermal shock resistance of the continuous casting nozzle of the present invention was evaluated by repeating a cycle of dipping the sample in molten steel at 1600 ° C. for 90 seconds, water cooling for 15 seconds, and air cooling for 60 seconds. Evaluation of the test at this time is 3
Those that did and did not come off at the 0th time ◎ 2
What was peeled off from the 5th to 29th time was marked with ◯, and what was peeled off less than 25 times was marked with x.

On the other hand, Table 2 shows a comparative example for this.

[0030]

[Table 2]

Also in this case, the modified pitch or phenolic resin dissolved in an organic solvent was added as a binder to 100% by weight of the raw material composition, followed by kneading, rubber press molding, drying (90 ° C. × 24 hours), Reduction firing (13
(00 ° C. × 3 hours) was carried out to manufacture a nozzle for continuous casting. Here, similarly to the above-mentioned examples, fused alumina, sintered alumina, fused zirconia, sintered zirconia, fused calcium zirconate were used as the refractory oxide, and flake graphite having a purity of 99% was used as the carbon material. Powder is Al and S
i was used. Toluene, which is an aromatic compound, and quinoline, which is a heterocyclic compound, were used as the organic solvent.

In addition, the thermal shock resistance of the continuous casting nozzle of this comparative example was evaluated in the same manner by using 1600 samples per time.
Immersion in molten steel at 90 ° C. for 90 seconds, water cooling for 15 seconds, and air cooling for 60 seconds were repeated until peeling. The evaluation of the test at this time was ◎ for those that peeled off at the 30th time and those that did not peel off, and ○ for those that peeled off at the 25th to 29th times.
What was peeled off less than 25 times was designated as x. As is clear from Table 1, all the continuous casting nozzles obtained by the production method of the present invention exhibit excellent thermal shock resistance. On the contrary,
The comparative examples shown in Table 2 are inferior in thermal shock resistance.

(Example 2) Sample No. 1 of Example 1 5
The firing temperature was changed as shown in Table 3. The evaluation is that the bending strength of 20 MPa or more is ◯, 20MP
Those less than a were rated as x. As is clear from Table 3, the continuous casting nozzles obtained by the manufacturing method of the present invention are all excellent in strength. On the other hand, the comparative example is inferior in strength.

[0034]

[Table 3]

(Example 3) Sample No. 1 of Example 1
With respect to Nos. 2, 4, and 7, the method of adding the modified pitch was changed as shown in Table 4. In the evaluation, those having a bending strength of 20 MPa or more were evaluated as O, and those having a bending strength of less than 20 MPa were evaluated as X. As is clear from Table 4, the continuous casting nozzles obtained by the manufacturing method of the present invention are all excellent in strength. On the contrary,
The comparative example is inferior in strength.

[0036]

[Table 4A]

[0037]

[Table 4B]

[0038]

According to the present invention, the following effects can be obtained. It is possible to improve the thermal shock resistance, which was a technical barrier for the conventional continuous casting nozzle, and it is possible to reduce the cost of the continuous casting nozzle and to reduce the work cost by relaxing the preheating conditions.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amount of modified pitch added and bending strength in the results of experiments conducted using fused alumina and scaly graphite.

[FIG. 2] FIG. 2 shows a case where metal A is used with fused alumina and scaly graphite.
Regarding the result of the experiment conducted by adding the powders of 1 and Si,
It is a figure showing the relation between the amount of metal added and bending strength.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI technical display location B22D 41/54 C04B 35/00 35/52 // C04B 35/103 C04B 35/52 B 35/10 G (72 ) Inventor Takeshi Matsui 1 Nishinosu, Oita-shi, Oita New Nippon Steel Co., Ltd. Oita Works

Claims (5)

[Claims] 1. A solution prepared by dissolving 2 to 4% by weight of modified pitch in an organic solvent is added to a mixture 100 containing a refractory oxide and a carbon material as main components, and then mixed. A method for producing a nozzle for continuous casting, which comprises molding, drying and firing. 2. A refractory oxide and a carbon material as main components,
To the compound 100 in which Al or Si powder was added thereto, a solution in which 2 to 4% by weight of modified pitch was dissolved in an organic solvent was added, mixed, molded, dried, and fired. A method for manufacturing a continuous casting nozzle, comprising: 3. The modified pitch is soluble in an organic solvent,
Use of a crystalline phase or a mixed phase composed of a crystalline phase and an amorphous phase and having a weight loss rate of 30% or less when fired at 800 ° C. in a non-oxidizing atmosphere. The method for manufacturing a nozzle for continuous casting according to claim 1, which is characterized in that. 4. An organic solvent comprising an aromatic compound or a heterocyclic compound is added in an amount of 2 to 1 with respect to 100 parts by volume of the mixture.
The method for producing a continuous casting nozzle according to claim 1, 2 or 3, wherein 0 volume% is added. 5. The method for producing a continuous casting nozzle according to claim 1, wherein the firing is performed within a range of 1200 to 1400 ° C.