JPH05309457A - Refractory for continuous casting - Google Patents

Abstract

PURPOSE:To obtain a material having sticking resistant alumina in a steel in comparatively low cost by making the specific ratios of a carbonaceous raw material, a refractory raw material and a cryolite in a refractory used for a continuous casting machine. CONSTITUTION:This refractory for continuous casting is composed of 10-50wt. parts carbonaceous raw material, 50-90wt, parts refractory raw material and 0.5-10wt. parts cryolite having chemical composition of Na3AlF6 or the mixed material of NaF and AlF3. In this case, for the carbonaceous raw material, flake graphite, earthy graphite, coke or carbon black are used and for the refractory raw material, alumina, magnesia, zirconia or spinel are used. Thus, by applying the refractory composed of the above-mentioned materials to an immersion nozzle 10 for continuous casting, the trouble, such as nozzle clogging caused by the alumina in the steel, defective stopping operation of the molten steel caused by the sticking of the alumina in the connecting part between a stopper head and an upper nozzle is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory for continuous casting, which is used for injection nozzles, stopper heads and the like in a steel continuous casting machine and which suppresses adhesion of alumina to the surface.

[0002]

2. Description of the Related Art In continuous casting of steel, refractory materials are used as stopper heads and nozzles for supplying molten steel from a tundish to a mold. Here, the dip nozzle inserted into the mold will be described in detail. This refractory material has functions of supplying molten steel, preventing oxidation of the molten steel, preventing disturbance of the molten steel flow during casting, and preventing slag inclusion. Therefore, it plays an important role in improving the quality by reducing the non-metallic inclusions in the obtained slab.

Further, the immersion nozzle is required to have a high level of spalling resistance, wear resistance and corrosion resistance due to its use conditions, and conventionally, as a material corresponding thereto, Al ₂ O ₃ -C has been used.
A structure using a ZrO ₂ —C material, which has a _high quality and is excellent in corrosion resistance, is widely used in the molten metal level portion in the mold. Even in dipping nozzles using these materials, nozzle narrowing or blockage due to alumina adhesion is a problem.

This is particularly noticeable in the casting of aluminum-killed steel and aluminum-silicon-killed steel, and alumina, which is a deoxidizing product in the steel, adheres to the inner wall surface of the inner hole of the immersion nozzle and gradually grows to narrow the inner hole. However, in the end, nozzle clogging often occurs, which not only lowers the durability of the nozzle, but also deteriorates the quality of the cast slab obtained when such an adhered product is captured by the molten steel.

[0005]

In order to prevent the narrowing or blockage of the nozzle inner hole portion due to such alumina adhesion, an inert gas such as argon gas is blown out from the nozzle inner hole portion to physically It is widely practiced to prevent the adhesion. However, even by this means, when the continuous casting operation is continued, it is often impossible to completely prevent the adhesion and growth of non-metallic inclusions such as alumina. In addition, depending on the type of steel, blowing the argon gas itself may not be desirable for the product, and it is not a sufficient countermeasure.

As another means, there is also a method of preventing clogging of the nozzle by using a material that is difficult to adhere to alumina for the immersion nozzle. For example, Japanese Patent Application Laid-Open No. 4-28462 discloses electrofusion Z.
An immersion nozzle applying a ZrO ₂ —CaO—C material using an rO ₂ —CaO raw material, and JP-A-3-4761 proposes a method of applying it to a stopper head or an upper nozzle to prevent alumina adhesion. ing. In these, CaO in the ZrO ₂ -CaO raw material precipitates during use and reacts with Al ₂ O ₃ which is a non-metallic inclusion in the molten steel to form calcium aluminate having a low melting point, and is washed by the molten steel flow to an appropriate degree. The purpose is to renew the surface of the refractory and to prevent the growth of adhered and deposited alumina by imparting sufficient melting loss.

[0007] ZrO ₂ -CaO raw materials used herein are those that produce mineral is composed of cubic ZrO ₂ and ZrCaO _3, Zr added with normal CaO
It is an electrofusion clinker obtained by electrofusion of O ₂ . Therefore, the cost of ZrO ₂ —CaO—C material is higher than that of gas blow type Al ₂ O ₃ —C material, which is widely used due to the use of expensive electro-melting raw material, which is a difficulty in industrial spread. There is. The present invention is intended to provide a material in which alumina in steel hardly adheres at a relatively low cost.

[0008]

As a result of various experiments to solve the above problems, the present inventors have found that a commonly used refractory containing carbon has cryolite (Na ₃ Al).
It has been found that the addition of F ₆ ) can prevent the adhesion of alumina.
0 parts by weight, refractory raw material 50 to 90 parts by weight, cryolite 0.5 to
A refractory for continuous casting characterized by having a composition of 10 parts by weight, and NaF and AlF instead of cryolite.
It is intended to provide a refractory material in which 1 or 2 of ₃ is mixed. In the latter case, the composition ratio of NaF to AlF ₃ is close to that of cryolite, so that the molar ratio is preferably 3: 1.

The carbon raw material used in the present invention is optimal for improving slag erosion resistance and spalling resistance due to high thermal conductivity, and further, flake graphite optimal for filling properties and molten steel resistance, One or two of earthy graphite, coke and carbon black is used.

As a refractory raw material, it has excellent slag resistance,
It is composed of one or more species of alumina, zirconia, magnesia, spinel, etc., which have the characteristic of being hard to reduce and disappear even in a high temperature atmosphere. That is, Al ₂ O ₃ −
_{C, ZrO 2 -C, MgO-} C, MgO-Al 2 O 3 -C
Any of these may be used, but in view of spalling resistance and cost, those based on Al ₂ O ₃ —C quality are preferable.

The method for producing a refractory for continuous casting according to the present invention comprises:
For example, 10 to 50 parts by weight of scaly graphite, 50 to 90 parts by weight of alumina refractory raw material, and 0.5 to 10 parts by weight of cryolite are mixed, and an organic binder of pitch and resin is added to this mixture and kneaded and added. The press-molded product is dried, and then fired in a non-oxidizing atmosphere to obtain the refractory material for continuous casting of the present invention.

Here, the carbon raw material is set to 10 to 50 parts by weight. If the amount is less than 10 parts by weight, the spalling resistance is insufficient, and if it exceeds 50 parts by weight, the corrosion resistance is deteriorated.
It was 50 parts by weight. Needless to say, when alumina is used as the refractory raw material, any of sintered alumina, fused alumina and β-alumina can be used.

In the present invention, cryolite or Na
F, the mixing amount of AlF ₃ are 0.5 to 10 parts by weight, is less than 0.5 part by weight is insufficient alumina deposition preventing effect, low melting reaction product of more than 10 parts by weight This is because much of the corrosion resistance deteriorates. The present invention thus obtained is applied to the surface of an immersion nozzle, a stopper head, an upper nozzle, or the like, or to a portion of an inner hole where alumina is adhered to suppress the adhesion of alumina.

[0014]

Operation: The phase diagram of Na ₃ AlF ₆ -Al ₂ O ₃ shown in FIG.
has Diagrams Ceramis
t, (1964) P474], Na ₃ AlF
₆ is known to react with Al ₂ O ₃ to form a low melting point compound. The present invention was made based on this finding, and solves the drawbacks of conventional refractory materials by adding cryolite or a similar raw material at an appropriate composition ratio to carbon materials and refractory materials of appropriate materials and composition ratios. The idea was that it was possible.

That is, Al ₂ which is a non-metallic inclusion in molten steel
When O ₃ adheres to the refractory of the present invention, it reacts with cryolite or a similar raw material Na ₂ AlF ₆ to form a low-melting point compound, which is washed away by the molten steel flow, resulting in the refractory surface. The invention has led to the invention of an industrially extremely effective invention that can remove the adhered alumina.

To explain the mechanism in more detail, cryolite has a composition of Na ₃ AlF ₆ and its melting point is 1030 ° C.
As shown in Fig. 1, a low-melting liquid phase is formed with alumina, but the liquid phase does not evaporate in the temperature range from the firing temperature of bricks of 1000 ° C to the molten steel temperature of about 1600 ° C. Exists. Also NaF and AlF ₃
The reason why the effect similar to that of cryolite can be obtained by adding the mixture is also considered as follows. NaF has a melting point of 993 ° C.
The boiling point is as high as 1704 ° C., and AlF ₃ has a melting point of 1291 ° C. and is a substance which is difficult to decompose by heat. It is considered that neither of them decomposes or evaporates up to 1000 ° C., which is the firing temperature of bricks, and remains relatively stable up to the temperature at which it reacts with Al ₂ O _{3 in} steel.

[0017]

Example A sample of brick was prepared by using the raw materials shown in Table 1 and the composition shown in Table 2. After kneading the required amount of each material, it is molded with a rubber press at a pressure of 1000 kg / cm ² and dried at about 150 ° C. under a non-oxidizing atmosphere for 10 minutes.
It was baked at 00 ° C. The physical properties and characteristic values of the obtained brick are also shown in Table 2.

The measurement was carried out by the following method. a. Alumina adhesion test A test piece of 20 × 20 × 150 mm was cut out and immersed in a high frequency furnace in which 5 kg of steel was melted at 1580 ° C., and immediately after immersion, 15 minutes later, 30 minutes later, 10 aluminum pieces each.
Al ₂ O ₃ which is a deoxidation product was made in molten steel by adding g, and the alumina adhesion thickness was measured 60 minutes after the beginning. b. Molten steel erosion test A 20 × 20 × 150 mm test piece was attached to a crucible of a high-frequency furnace with mortar to melt the steel, and the molten steel was spun at 50 rpm with a stirring blade made of high alumina brick.
After stirring for 2 hours and holding at 1580 ° C. for 2 hours, the amount of erosion loss was measured. In both a and b tests, the molten steel surface was sealed with Ar gas.

In Table 2, formulation Nos. (1) to (8) are examples within the scope of the present invention, and (9) to (11) are comparative examples. (1) to (4) of the present invention are those in which cryolite is added to Al ₂ O ₃ -C as a base, and compared with the non-added Al ₂ O ₃ -C of (10) in Comparative Example, alumina is used. It is in a state close to ZrO ₂ —CaO—C of (11) without adhesion. However, as shown in (9), when the addition amount of cryolite is large, the corrosion resistance becomes poor and the hot strength becomes poor. Further, (5) is the addition of NaF and AlF ₃ instead of cryolite, which shows the same effect as cryolite. Further, (6) to (8) which are examples of the present invention include ZrO ₂ − in addition to Al ₂ O ₃ —C.
C, MgO-C, and spinel-C also show that the addition of cryolite has an alumina adhesion preventing effect.

When the microstructure of the sample of the present invention after the alumina adhesion test was examined by EPMA, the Al ₂
A low-melting film containing O ₃ -Na ₂ O as a main component is formed, and as described above, the low-melt material is generated on the working surface, so that it is washed by the molten steel flow and the refractory surface is constantly updated. Therefore, the adhered growth of alumina is suppressed.

Next, an embodiment of the present invention in an actual machine will be described. (Example 1) The product of the present invention shown in formulation No. (3) of Table 2 was applied to the immersion nozzle 10 having the structure shown in FIG. No. 1 of the present invention is provided on the lower part 1 of the nozzle including the discharge hole 4 and the wall surface 5 of the inner hole, that is, at least in the part in contact with the molten steel. 3 is used,
The outer upper part 2 of the nozzle is made of a conventional Al ₂ O ₃ -C refractory, and the powder line part 3 is made of a conventional ZrO ₂ -C refractory. When this immersion nozzle 10 was used for continuous casting of aluminum-killed steel, which was prone to alumina clogging even with the conventional gas blow type Al ₂ O ₃ -C quality immersion nozzle, alumina adhesion did not occur when using an average of 8 charges. It did not occur at all and was better than the conventional product.

(Example 2) The product of the present invention shown in formulation No. (2) of Table 2 was applied to the stopper head and the upper nozzle having the structure shown in FIG. When the stopper head 7 formed at the tip of the long stopper 6 and the upper nozzle 8 are joined to each other at the joint portion 9, the present invention No. 2 was used. In the second embodiment, the long stopper 6, the stopper head 7 and the upper nozzle 8 are used.
The joint part 9 and the peripheral main part are the products of the present invention, but a conventional refractory material (Al ₂ O ₃ -C quality refractory material in this case) was used except for the main part. When this stopper head and upper nozzle were used for continuous casting of aluminum-killed steel, which had been heavily adhered to alumina in the past, no alumina adhesion occurred at the joint, so problems such as defective molten metal stop that could occur at the end of casting It has become possible to completely eliminate it.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

EFFECT OF THE INVENTION Cryolite or NaF and AlF of the present invention
By applying refractory for continuous casting with the mixture of ₃ added in a specific range to the immersion nozzle, stopper head, upper nozzle, etc., alumina clogging of the nozzle and hot water stop due to alumina adhesion at the joint between the stopper head and upper nozzle Trouble in continuous casting such as defects can be prevented. Further, the same effect of preventing adhesion of alumina as that of the present invention can be obtained.
It becomes possible to provide a refractory for continuous casting at a lower cost than a ZrO ₂ —CaO—C quality refractory, and its industrial value is remarkable.

[Brief description of drawings]

FIG. 1 Na ₃ AlF ₆ —Al ₂ in the refractory material of the present invention
O ₃ system is a state diagram.

FIG. 2 is a vertical cross-sectional explanatory view of the immersion nozzle according to the first embodiment of the present invention.

FIG. 3 is a vertical cross-sectional explanatory view of a stopper head and an upper nozzle according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Nozzle lower part 2 Nozzle upper part outside 3 Powder line part 4 Discharge hole 5 Inner hole wall surface 6 Long stopper 7 Stopper head 8 Upper nozzle 9 Contact part 10 Immersion nozzle

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Inoue 12 Nakamachi, Muroran-shi, Hokkaido Inside Nippon Steel Co., Ltd. Muroran Works (72) Inventor Yoichi Yokoyama 1-3-1 Niihama, Arai-cho, Takasago, Hyogo Prefecture Harima Ceramic Co., Ltd. (72) Inventor Yoshinori Yamamoto 1-3-1 Niihama, Arai-cho, Takasago, Hyogo Prefecture Harima Ceramic Co., Ltd.

Claims (4)

[Claims] 1. A refractory used in a continuous casting machine, comprising 10 to 50 parts by weight of carbon raw material and 50 to 90 refractory raw material.
A refractory for continuous casting, characterized by comprising 1 part by weight and 0.5 to 10 parts by weight of cryolite. 2. The method according to claim 1, wherein one or two of NaF and AlF ₃ are mixed instead of cryolite.
Refractory for continuous casting described. 3. The refractory material for continuous casting according to claim 1, wherein the carbon raw material is one or more of scaly graphite, earthy graphite, coke and carbon black. 4. The refractory material for continuous casting according to claim 1, wherein the refractory raw material is one or more of alumina, magnesia, zirconia and spinel.