KR20010098628A - Immersion nozzle - Google Patents

Abstract

The present invention is an immersion nozzle that has corrosion resistance to a steel having a high oxygen content, a steel treated with calcium, and the like, and can prevent the deposition of molten steel and oxide inclusions on the inner wall of the nozzle. To provide.

At least a part of the portion in contact with the molten steel comprises at least 50% by weight, 0.3-15% by weight of boron nitride, and an organic binder in any one or two or more of main components of magnesia, alumina, spinel, zirconia, mullite, and silica. An immersion nozzle is used, comprising a refractory material containing a binder of.

Description

Immersion Nozzle {IMMERSION NOZZLE}

The present invention relates to an immersion nozzle. More specifically, the present invention relates to an immersion nozzle, such as an immersion nozzle, which introduces molten steel in a tundish into a mold in continuous casting, and has high corrosion resistance. It is related with the immersion nozzle which consists of a refractory material which suppresses adhesion and deposition of a nonmetallic inclusion to a wall now.

In continuous casting, immersion nozzles such as a long nozzle used between the ladle and the tundish, an air seal pipe, and an immersion nozzle for introducing molten steel in the tundish into the mold are used. These immersion nozzles are required to have characteristics such as fracture resistance, abrasion resistance, and corrosion resistance to molten steel or slag depending on their use environment.

Conventionally, in order to respond to this demand, alumina-graphite or alumina-silica-graphite or the like has been used as a fireproof material of the immersion nozzle.

However, in alumina-silica-graphite refractory materials, alumina and silica are eroded by FeO, CaO, etc. in casting of a kind of steel with a high oxygen content or a kind of calcium treated with calcium, and can withstand long-term use. There was a problem that there was not.

Therefore, fireproofing materials, such as alumina-graphite which reduced comparatively low corrosion resistance low silica, are used, but since oxidation resistance and corrosion resistance of graphite are low, this also does not acquire sufficient durability.

In addition, the alumina-graphite or alumina-silica-graphite refractory material has a problem that inclusions due to oxidation of aluminum in molten steel, slag, etc. adhere to the inner wall surface of the immersion nozzle, and the nozzle is likely to be clogged.

If the immersion nozzle is clogged, flow control of molten steel becomes impossible, making continuous casting difficult, and there is a problem that the quality of steelmaking is deteriorated by peeling off deposits on the inner wall of the immersion nozzle during operation. .

As a means of preventing the blockage of such an immersion nozzle, the method of blowing inert gas into an immersion nozzle is proposed. According to this method, oxide inclusions such as alumina agglomerates can be prevented from adhering to and deposited on the inner wall of the nozzle, but fine bubbles are formed in the molten steel by the blown gas, whereby the formation of pin holes, insertion of inclusions, etc. A defect may occur. Since this problem is caused by the formation of fine bubbles in molten steel, it is very difficult to solve.

On the other hand, as a means other than these, the immersion nozzle which consists of a refractory material containing 5 to 80% of boron nitride is proposed from the viewpoint of the material of an immersion nozzle, as disclosed by Unexamined-Japanese-Patent No. 56-139260. In addition, in recent years, as disclosed in Japanese Patent Laid-Open No. Hei 10-314905, an immersion nozzle containing no refractory material containing carbon or reducing carbon in order to prevent adhesion of alumina has been proposed.

By the way, the inventor of the present application pays attention to the material of the immersion nozzle which can be used as a solution as a means of preventing the blockage of the nozzle, and has made improvements to the conventional material.

That is, as described above, in the immersion nozzle made of a refractory material containing 5 to 80% of boron nitride as proposed in Japanese Patent Laid-Open No. 56-139260, since it is based on the use of graphite, corrosion resistance And technical problems that the effect on the prevention of occlusion is insufficient.

In addition, in the immersion nozzle which does not contain carbon or consists of the refractory material which reduced carbon, the effect which prevents an oxide inclusion, such as alumina, from adhering to a nozzle inner wall surface is recognized, but the effect which prevents adhesion of molten steel itself is inadequate. There was a technical problem to be said.

As mentioned above, in the technique focusing on the conventional material proposed as a means of preventing the blockage of a nozzle, various problems inherent, and the effect on the blockage prevention was not sufficient.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and has corrosion resistance to steels of high oxygen content or steels treated with calcium, and deposited with molten steel and oxide inclusions on the inner wall of the nozzle. It is an object of the present invention to provide an immersion nozzle which can prevent the use thereof.

1 is a cross-sectional view showing an example of the immersion nozzle for continuous casting according to the present invention.

2 is a cross-sectional view showing another example of the immersion nozzle for continuous casting according to the present invention.

<Explanation of symbols for main parts of drawing>

1: Nozzle body part

2: powder line part

3: nozzle inner wall part

4: nozzle outer wall

5: nozzle inner wall

Immersion nozzle according to the present invention is at least a portion of the portion in contact with the molten steel of at least 50% by weight, 0.3-15% by weight of any one or two or more of the main components of magnesia, alumina, spinel, zirconia, mullite, silica It is characterized by consisting of a refractory material containing a binder of boron nitride and an organic binder.

Since the refractory material has a low expansion rate and low wettability to molten steel, and boron nitride having excellent abrasion resistance and lubricity is used, it is possible to provide an immersion nozzle excellent in durability by preventing clogging of the nozzle.

In addition, the immersion nozzle according to the present invention is characterized in that a thick layer having a thickness of 2 to 15 mm is formed by the refractory material.

It is preferable that the said thick layer is formed in the above-mentioned thickness at least in the part which contact | connects molten steel from a viewpoint of the effect of blocking a nozzle and the structural peeling of a fireproof material.

Hereinafter, the present invention will be described in more detail.

Refractory material used for the immersion nozzle according to the present invention is a total of any one or two or more of the main components of magnesia, alumina, spinel, zirconia, mullite, silica, 50% by weight, 0.3-15% by weight of boron nitride, It is characterized by containing a binder of the organic binder.

In this way, by containing boron nitride in the refractory material, breakage such as cracking and cracking is less likely to occur, and an immersion nozzle capable of preventing deposition of molten steel and oxidative inclusions on the nozzle inner wall surface can be obtained. The boron nitride also has a low expansion ratio, low wettability to molten steel, and excellent wear resistance and lubricity.

When content of boron nitride in the said refractory material is less than 0.3 weight%, sufficient lubricity cannot be acquired in a refractory material. On the other hand, when the content of boron nitride in the refractory material exceeds 15% by weight, the sinterability of the refractory material is lowered, resulting in a decrease in strength, and at a high cost.

In the fireproof material, any one or two or more of magnesia, alumina, spinel, zirconia, mullite and silica are contained as main components.

The magnesia, spinel, zirconia and mullite have a high thermal expansion rate, which may cause damage such as cracking and cracking of the refractory material during use of the nozzle. However, these oxide-based materials have high melting point and high hardness, and are superior in corrosion resistance to FeO and CaO as compared to alumina or silica.

Therefore, by mixing a predetermined amount of a binder of boron nitride and an organic binder in these oxide materials, the thermal expansion rate can be reduced, and a nozzle which is difficult to break and excellent in corrosion resistance can be obtained.

The magnesia, alumina, spinel, zirconia, mullite, and silica may preferably contain 50% by weight or more of any one or two or more of the main components.

If the content of any one or two or more of the magnesia, alumina, spinel, zirconia, mullite, and silica is less than 50% by weight, sufficient corrosion resistance of the fireproof material cannot be obtained. Moreover, it is preferable to contain a silica for the purpose of the extinguishing prevention of the said magnesia, and it is preferable that content of the said silica is smaller than content of magnesia.

The refractory material used for the immersion nozzle according to the present invention does not contain graphite, unlike a nozzle such as conventional alumina-graphite. Therefore, no oxidizing gas is generated by the reaction between graphite and other compound in the refractory material during use, and aluminum in the molten steel is not oxidized, thereby preventing the formation of alumina. As a result, high quality steelmaking can be obtained.

In addition, the refractory material contains the binder of the organic binder. Thus, the binder of the organic binder is included in order to reduce the expansion rate of the refractory material and to prevent breakage such as cracking and cracking during use of the nozzle. In addition, an organic binder is not specifically limited, What is normally used may be used, such as a phenol resin.

In addition, it is preferable that the said fireproof material is formed as a thick layer of 2-15 mm in thickness in the part which contact | connects the molten steel of an immersion nozzle.

If the thickness of the thick layer is less than 2 mm, the corrosion resistance is not sufficient, and the effect of preventing the blockage of the nozzle is also insufficient. On the other hand, when the thickness of a thick layer exceeds 15 mm, there exists a possibility that a fireproof material may cause structural peeling.

In addition, the thick layer need not be formed in every part of the portion in contact with the molten steel, and may be formed in the nozzle inner wall portion at least in order to achieve the effect of preventing the blockage of the nozzle.

Moreover, the structure of the immersion nozzle which concerns on this invention is not specifically limited, As an example of a structure of the fireproof material in an immersion nozzle, the example as shown in FIG. 1 or 2 is mentioned.

That is, as shown in Fig. 1, the nozzle body portion 1 of the immersion nozzle is made of alumina-graphite refractory material commonly used for the immersion nozzle, and the powder line part 2 is made of zirconia-graphite refractory material. . Further, thick layers made of boron nitride-containing refractory material according to the present invention are formed in the nozzle inner wall portion 3, the nozzle outer wall portion 4, and the nozzle inner cavity wall 5 of the immersion nozzle.

In addition, in FIG. 2, only the inner wall part 3 of a nozzle is formed with the thick layer of the boron nitride containing fireproof material which concerns on this invention.

Although the manufacturing method of the immersion nozzle which concerns on this invention is not specifically limited, The following method can be illustrated.

First, each raw material of a fireproof material is kneaded with a mixer etc. The obtained dough is filled into a molding die and molded by CIP molding, mold press, or the like. The molded article thus obtained is dried and then fired in a non-oxidizing atmosphere. After baking, it can be processed into a final shape by processing as necessary to obtain a desired immersion nozzle.

Moreover, since the refractory material used for the immersion nozzle which concerns on this invention contains boron nitride, the dough of the raw material is excellent in lubricity, and even when compared with the refractory material which does not contain carbon, it is excellent in workability at the time of shaping | molding.

Therefore, it is also possible to integrally mold the inner wall portion of the nozzle body made of alumina-graphite refractory material. Accordingly, structurally, the fracture resistance can be improved.

Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.

Example 1

Each blend composition as shown in Sample Nos. 1 to 4 of the present invention in Table 1 was placed in a nozzle body consisting of 36 wt% alumina, 30 wt% graphite, 25 wt% organic binder, and 9 wt% silicon carbide. The fireproof material was provided in the inner wall part of the immersion nozzle as a thick layer of thickness 5mm, and the immersion nozzle as shown in FIG. 2 was produced.

Using this immersion nozzle, the casting test was done in the actual furnace. The kind of steel used what is Al content 0.03 weight%. As a continuous casting machine, using the two strand mold, the immersion nozzle was attached to No. 1 strand, and the casting test of 5 ch (casting time about 170 minutes) was performed 5 times.

After the test, the thickness of the deposits at three cross sections in the direct trunk portion of the nozzle was measured, and the average value was obtained. The average value over 5 tests of the average value is shown in Table 1 as deposit thickness.

Comparative Example 1

A thick layer was formed by immersion nozzles consisting of a compound composition as shown in Comparative Sample No. 1 of Table 1, namely 36% by weight of alumina, 30% by weight of graphite, 25% by weight of organic binder, and 9% by weight of silicon carbide. It produced without making it, attach it to the No. 2 strand of a continuous casting machine, and performed the casting test.

Table 1 shows the deposit thickness measured in the same manner as in Example 1.

Compounding composition (% by weight) Attachment thickness (mm) Boron nitride magnesia Alumina Spinel Zirconia Silica Organic Binder black smoke Silicon Carbide Example Sample Number One One 4 84 - - One 10 - - 1.0 2 5 - - 85 - - 10 - - 0.8 3 10 - - - 80 - 10 - - 0.5 4 10 39 - 40 - One 10 - - 0.9 Comparative Example Sample Number One - - 36 - - - 25 30 9 13.7

As shown in Table 1, with respect to samples Nos. 1 to 4 of the present invention, the deposit thickness was 1 mm or less, and the effect of reducing the deposit deposit was less than 1/10 of the comparative sample No. 1.

Example 2

Each blend composition as shown in Sample Nos. 1 to 5 of the present invention in Table 2 in a nozzle body composed of 36 wt% alumina, 30 wt% graphite, 25 wt% organic binder, and 9 wt% silicon carbide. Refractory material was provided as a thick layer having a thickness of 5 mm in the inner wall portion of the immersion nozzle to produce an immersion nozzle as shown in FIG.

Using this immersion nozzle, casting test was carried out in an actual furnace. High oxygen steel (oxygen concentration: 200 ppm) was used as the type of steel. As a continuous casting machine, using the two strand casting mold, the immersion nozzle was attached to No. 1 strand, and the casting test of 1 ch (casting time about 60 minutes) was performed three times.

After the test, the maximum melt damage thickness of the inner wall portion in the direct trunk portion of the nozzle was measured. The value is shown in Table 2.

Comparative Example 2

The immersion nozzle which consists of each compounding composition as shown to the comparative samples No. 1-5 of Table 2 was produced without forming a thick layer.

This immersion nozzle was attached to the No. 2 strand of continuous casting, and the casting test was done on the conditions similar to Example 2.

After the test, the maximum melt damage thickness of the inner wall portion in the cross section of the direct body portion of the nozzle was measured. The value is shown in Table 2.

Compounding composition (% by weight) Melt damage thickness (mm) Boron nitride magnesia Alumina Spinel Zirconia Silica Organic Binder black smoke Silicon Carbide Example Sample Number One One 4 84 - - One 10 - - 0.5 2 5 - - 85 - - 10 - - 0.2 3 10 - - - 80 - 10 - - 0.1 4 10 39 - 40 - One 10 - - 0.2 5 10 4 75 - - One 10 - - 0.6 Comparative Example Sample Number One - - 36 - - - 25 30 9 23 2 10 4 45 - - One 10 30 - 22 3 10 4 65 - - One 10 10 - 20 4 10 4 70 - - One 10 5 - 13 5 10 4 74 - - One 10 One - 7

As shown in Table 2, in continuous casting of high oxygen steel, the maximum melt damage thickness of the inner wall surface of the immersion nozzle is 0.6 mm or less for the samples Nos. 1 to 5 of the examples, and Comparative Examples Nos. 1 to 5 Corrosion resistance to high oxygen steels was improved to less than 1/10 of.

In particular, Comparative Examples Sample Nos. 1 to 4 containing 5% by weight or more of graphite showed that the maximum melt damage thickness was 20 times or more than that of the example samples, so that the corrosion resistance of the refractory material containing graphite was low.

Therefore, it was confirmed that the sample of the Example which does not contain graphite has high corrosion resistance with respect to high oxygen steel compared with the comparative example sample which is a conventional product.

Example 3

Each blend composition as shown in Sample Nos. 1 to 5 of the present invention in Table 2 in a nozzle body composed of 36 wt% alumina, 30 wt% graphite, 25 wt% organic binder, and 9 wt% silicon carbide. Regarding the fire resistant material, the inner wall portion of the immersion nozzle was provided as a thick layer having a thickness of 5 mm to prepare an immersion nozzle as shown in FIG. 2.

Casting test was done on the conditions similar to Example 2 using this immersion nozzle.

After the test, the porosity of the nozzle was measured by JIS R 2205 "Measurement method of external appearance porosity of fire brick, water absorption-specific gravity". In addition, the bending strength was measured by JIS R 2213 "Test method of the bending strength of a firebrick". This porosity and bending strength are shown in Table 3.

Comparative Example 3

In the nozzle body which consists of 36 weight% alumina, 30 weight% graphite, 25 weight% organic binder, and 9 weight% silicon carbide, the fireproof material of each compounding composition as shown to the comparative samples No.6 and 7 of Table 3 In this regard, the inner wall portion of the immersion nozzle was provided as a thick layer having a thickness of 5 mm to produce an immersion nozzle as shown in FIG. 2.

The porosity and the bending strength of this nozzle were measured in the same manner as in Example 3. This porosity and bending strength are shown in Table 3.

Compounding composition (% by weight) Porosity (%) Bending strength (MPa) Boron nitride magnesia Alumina Spinel Zirconia Silica Organic Binder black smoke Silicon Carbide Example Sample Number 5 10 4 75 - - One 10 - - 18.7 15 Comparative Example Sample Number 6 20 4 65 - - One 10 - - 24.6 2.6 7 30 4 55 - - One 10 - - 36.7 1.4

As shown in Table 3, while the porosity of sample No. 5 of the present invention was 18.7%, both of Comparative Examples Nos. 6 and 7 containing 20 wt% or more of boron nitride were as high as 20% or more.

Accordingly, the bending strengths of the nozzles were lower than Comparative Sample Nos. 6 and 7 to less than 1/5 of Sample No. 5 of the examples.

Therefore, as the content of boron nitride increases, the porosity increases, and accordingly, the bending strength of the nozzle is lowered, and when it exceeds 15% by weight, it was confirmed that sufficient strength of the nozzle could not be obtained.

As mentioned above, when the immersion nozzle which concerns on this invention is used, corrosion resistance to the kind of steel with high oxygen content, the kind of steel processed with calcium, etc. can be improved.

In addition, it is possible to prevent deposition of molten steel, oxide inclusions, and the like on the nozzle inner wall surface to prevent clogging of the nozzle, thereby enabling continuous use of the nozzle for a long time.

Therefore, by using the immersion nozzle according to the present invention, labor and time required for maintenance of the nozzle in the casting process and the like can be reduced, and further, high quality steelmaking can be obtained even in high oxygen steel and the like.

Claims (2)

At least a part of the portion which is in contact with the molten steel comprises at least 50 wt%, 0.3-15 wt% of boron nitride and a binder of magnesia, alumina, spinel, zirconia, mullite and silica in total. An immersion nozzle, comprising a refractory material containing a binder. The immersion nozzle according to claim 1, wherein a thick layer having a thickness of 2 to 15 mm is formed of the refractory material.