JPH07214256A - Nozzle for continuous casting - Google Patents

Abstract

(57) [Summary] [Objective] The present invention relates to a nozzle structure for improving the durability of a refractory material used in the vicinity of an interface (slag line portion) in contact with a meniscus portion of a molten metal between a long nozzle for continuous casting and a dipping nozzle. By providing a refractory structure that satisfies the contradictory characteristics of spall resistance and corrosion resistance at the same time, we have improved durability. [Structure] A triple structure refractory in which the highly corrosion resistant refractory is embedded inside the high spall resistant refractory.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a long nozzle used for continuous casting of molten metal (a nozzle used when pouring molten metal from a ladle into a tundish) and an immersion nozzle (molten metal is poured from a tundish into a mold). Nozzle used when injecting) relates to a nozzle for continuous casting in which the durability of a nozzle refractory used in a portion (slag line portion) in contact with a molten metal meniscus portion is improved.

[0002]

2. Description of the Related Art The quality characteristics required for refractory materials used for long nozzles and immersion nozzles that come into direct contact with high-temperature molten metal or slag are excellent heat spalling resistance and high corrosion resistance. Both of these nozzles are used by immersing them in molten metal or slag, but especially the refractory located in the slag line part of the nozzle is not only melted by the hot molten metal in the nozzle inner hole, but also the outer surface of the nozzle. Is also eroded by the oxide component having strong chemical erosion property in the slag floating on the surface of the molten metal.

As described above, the refractory in the nozzle slag line is damaged from the inside and the outside at the same time, and is the portion having the lowest durability in the entire nozzle. Therefore, although the other parts can be used sufficiently, the entire nozzle has been discarded due to the low durability of the slag line part. Therefore, for the nozzle slug line portion, a shape that is thicker than other portions has been adopted, but it has not been a sufficient countermeasure. Attempts have also been made to use a material having a higher corrosion resistance than that of the other portions for this portion. For example, in Japanese Utility Model Publication No. 55-32699, the nozzle body is made of alumina-graphite refractory, and the nozzle slag line part is made of zirconia-graphite refractory showing superior slag corrosion resistance to alumina-graphite refractory. Proposals have been made to improve the durability of the nozzle by configuring it.

[0004]

As a general feature of refractory materials, corrosion resistant refractory materials tend to have poor spalling resistance, while spalling resistant refractory materials tend to have poor corrosion resistance. Even if a corrosion-resistant refractory material is used for the nozzle slag line, the nozzle refractory material is rapidly heated when it comes into contact with high-temperature molten metal in the early stages of casting, causing spalling due to the thermal stress that occurs, leading to cracking. There is. Therefore, for the refractory used in the slag line part of the continuous casting nozzle,
Although there is a strong demand for corrosion resistance, the refractory materials to be actually used have been selected with a focus on refractory materials having spalling resistance.

Specifically, alumina-graphite refractory and zirconia-graphite refractory containing 20 to 30% by weight of scaly graphite as a carbon source are predominant.
The graphite content of this level is too high in terms of maintaining the corrosion resistance, and cannot be said to be sufficient. In order to avoid spalling, a nozzle using such a material for the slag line portion is generally used after being preheated to a high temperature by a gas burner or the like before using the nozzle. However, since the preheating temperature is lower than the molten metal temperature, there is a problem that it cannot be said to be sufficient as a measure against spalling.

A zirconium boride-containing refractory material is generally known as a material having both excellent corrosion resistance and spalling resistance. However, zirconium boride is an extremely expensive raw material, and in addition, it is necessary to cut and finish the outer periphery in order to obtain a predetermined dimension after firing a material molded by a rubber press. At this time, since many parts are scrapped, when a large amount of zirconium boride-containing refractory material is used as the nozzle refractory material, the cost of the nozzle becomes very high.

[0007]

SUMMARY OF THE INVENTION In view of the above problems, the present invention has a contradictory characteristic of corrosion resistance and spalling resistance required for a refractory in a slag line portion of a long nozzle or a dipping nozzle used for continuous casting. It is intended to improve the durability of the refractory material in the slag line portion without deteriorating the heat resistance and using a large amount of expensive raw materials.

[0008] Specifically, the refractory structure of the slag line portion has a characteristic, and its technical means is a portion (slag line portion) where the continuous casting nozzle contacts the molten metal meniscus portion.
In the refractory structure of No. 2, the nozzle for continuous casting is characterized in that the inner and outer walls of the nozzle are made of a spall resistant refractory layer and the middle portion thereof is made of a corrosion resistant refractory layer.

Here, the refractory constituting the spall resistant refractory layer is an alumina-graphite refractory or zirconia-graphite refractory containing 20-30 wt% of scaly graphite, and the corrosion resistant refractory layer. In the corrosion resistance test conducted under the same conditions, the refractory constituting the above-mentioned refractory constituting the spall-resistant refractory layer has a melting loss index of 100,
It is characterized by exhibiting a melt loss index of 80 or less.

A concrete refractory which constitutes the corrosion resistant refractory layer is any one of the following refractories containing 1 to 15% by weight of scaly graphite. Alumina-graphite refractory Alumina-zirconium boride-graphite refractory Zirconium boride-graphite refractory Zirconia-graphite refractory Zirconia-zirconium boride-graphite refractory

Further, regarding the thickness relationship between the spall resistant refractory layer on the inner and outer walls of the nozzle and the corrosion resistant refractory layer on the middle portion, the thickness in the radial direction from the nozzle inner hole surface to the nozzle outer surface is T,
The thickness of the corrosion-resistant refractory layer in the middle part is t1, the thickness of the spall-resistant refractory layer from the nozzle outer wall surface side to the middle part of the corrosion-resistant refractory layer is t2, and the corrosion-resistant refractory layer in the middle part from the nozzle inner hole surface The thickness of spall resistant refractory reaching the surface is t
When it is set to 3, it is necessary to satisfy the relationship of the following formula (1).

[0012]

Here, the slag line portion generally indicates a range of about ± 50 to 100 mm from the meniscus portion where the nozzle is in contact with the molten metal. Regarding the positional relationship between the corrosion-resistant refractory to be embedded in the slag-in portion and the surrounding spalling-resistant refractory, t2 and t3 are set to 5 mm or more when the thickness of the spalling-resistant refractory in contact with the high-temperature molten metal is small. The reason is that spalling cannot be prevented and cracks or falling off of the surface refractory material occur.

Generally, the radial thickness T of the spalling resistant refractory used for the refractory of the slag line portion of the long nozzle or the immersion nozzle is about 30 mm, and the thickness t1 of the corrosion resistant refractory to be buried is about 20 mm or less. . But t
In the case where No. 1 cannot secure a sufficient thickness, the refractory in the slag line portion is mainly spalling refractory, and there is not much difference from the conventional structure, so the lower limit of t1 is 3 mm. The spall-resistant refractory contains 20-30% by weight of scaly graphite that has been used in the slag line section.
Alumina-graphite refractory containing or zirconia-graphite refractory.

Further, the corrosion-resistant refractory to be buried needs to have a characteristic that the corrosion resistance is superior to that of the spall-resistant refractory. Corrosion resistance is evaluated by a commonly used rotary erosion tester or the like, and it is necessary to compare the spallation index of spall resistant refractory and corrosion resistant refractory under the same conditions. If the corrosion resistance of the spall resistant refractory is 100 or less, the corrosion resistance of the refractory can be expected to have a sufficient effect of improving the corrosion resistance.

There are several conceivable methods for manufacturing such a refractory structure, but there are the following methods, for example.
Highly corrosion-resistant refractory is pre-formed into a predetermined cylindrical shape, embedded in refractory powder that forms the slag line part, and the powder material and pre-forming material are molded by a rubber press and integrated. The method is effective. Alternatively,
When molding with a rubber press, it is also possible to divide and dispose different materials with a separator and then mold and integrate them.

[0017]

The graphite content as the carbon source of the refractory material generally used for the molten metal casting nozzle is 20% as described above.
It is about 30% by weight and the corrosion resistance is low. On the other hand, according to recent research, it has been found that when the amount of graphite is changed from 15% by weight to 1% by weight, the spalling resistance is lowered, but the corrosion resistance is remarkably improved. If it is 1% by weight or less, the spalling resistance of the refractory material is significantly deteriorated, so that it cannot be used as a nozzle for continuous casting.

Therefore, it is necessary to use such a low-graphite refractory material in the slag line portion and to obtain a refractory structure that is resistant to spalling in order to enjoy the effect of improving corrosion resistance. Further, even for a highly corrosion-resistant refractory whose outer periphery needs to be cut and finished to obtain a predetermined dimension after firing, if the refractory structure does not require strict dimensional accuracy, there is no need to finish the surface.

In order to effectively use such a corrosion resistant refractory material in the nozzle slag line portion, the present invention has developed a refractory structure for the slag line portion as described above. That is, the present invention has found that an effective refractory structure has a triple structure in which the corrosion resistant refractory layer 2 is arranged in the spalling resistant refractory layer 1 or 3 as shown in FIG. is there.

In FIG. 1, T is the radial thickness from the inner surface of the nozzle to the outer surface of the nozzle, t1: the thickness of the corrosion resistant refractory layer 2 in the middle portion, t
2: Thickness of spall resistant refractory layer 1 or 3 extending from the nozzle outer wall surface side to the intermediate corrosion resistant refractory layer surface, t3: Spall resistant refractory extending from the nozzle inner hole surface to the intermediate corrosion resistant refractory layer surface The thickness is 1 or 3.

The corrosion-resistant refractory layer of the intermediate layer thus arranged is indirectly and gently heated by the molten metal via the surrounding spalling-resistant refractory layer, so that the thermal stress is relaxed. As a result, it is possible to prevent the spalling problem at the initial stage of casting, which is one of the main reasons that the long durability of the corrosion resistant refractory layer is hindered. Once the continuous casting nozzle is used, it will continue to be used until its life. Therefore, if spalling at the time of preheating or at the beginning of casting can be avoided, the problem of spalling will not occur in the subsequent usage state.

Further, as the use time elapses, the spalling-resistant refractory layer covering the surface of the slag line part is progressively melted and the corrosion-resistant refractory layer disposed inside is exposed. Even if the corrosion-resistant refractory layer comes into direct contact with the molten metal or the slag, the corrosion resistance originally possessed by the refractory works to strongly suppress the erosion by the molten metal or the slag. Therefore, by adopting such a refractory structure in the slag line portion of the casting nozzle, the cracking problem due to spalling and the corrosion resistance problem due to molten metal or slag can be solved simultaneously and efficiently.

[0023]

EXAMPLE An example of a continuous casting nozzle having a structure to which the present invention is applied will be described below in comparison with an example of a conventional structure nozzle. The molten metal used in the examples was molten steel, which is a typical molten metal. These nozzles were applied to a continuous casting process in which molten steel is actually used to manufacture steel, and durability (number of nozzle durable channels) was compared. Further, the radial thickness T of the nozzles used was all 30 mm.

Tables 1 to 4 show examples and comparative examples of the present invention applied to long nozzles. Tables 1 and 2 show the components of the spall resistant refractory and the corrosion resistant refractory used in the examples, and the results of the rotary erosion test. Here, the rotary erosion test was performed as follows. [20 × 20 × 15 in the crucible in the high frequency furnace
A 0 mm test piece was attached with mortar, molten steel was put into a crucible, and the molten steel was stirred at 50 rpm with a stirring blade made of high alumina bricks, and then at 1580 ° C. for 2 hours.
After holding for a period of time, the melt loss amount (mm) of the test piece was measured. After that, the amount of melting loss of the spall resistant material was set as 100 and indexed, and the corrosion resistance of each material was evaluated. ]

As shown in Table 1, the spall-resistant refractory used in this rotary erosion test is an alumina-graphite refractory (scaly graphite: 25% by weight, alumina) used in the slag line of the conventional structure nozzle. 75% by weight) was used.

As shown in Table 2, nine types of corrosion-resistant refractory to be buried are listed for each component, but the following three types are basic systems. Alumina-graphite refractory: (1), (2), (3),
(4), (8), (9) -Alumina-zirconium boride-graphite refractory: (5) -Zirconium boride-graphite refractory: (6), (7) Here, from (1) The materials up to (7) are within the range of the present invention, but the materials of (8) and (9) are out of the range.

Further, FIG. 2 shows a sectional image view of long nozzles of the embodiment of the present invention and a comparative example, and FIG. 3 shows a sectional image view of long nozzles of a conventional example. 2 and 3, 1 is a high heat resistant spalling material and 2 is a high corrosion resistant material (embedding material).

Table 3 shows the practical data of the examples of the present invention.
Contents of combination of corrosion resistant refractory and spall resistant refractory,
The thickness t1, t2, t3 of each refractory and the obtained service c
The h number is shown.

In Table 4, the actual data of Comparative Example and Conventional Example are shown in the same manner as Table 3. Durable ch of nozzle using conventional material
The number was 17 ch as shown by S in Table 4. Inventive Examples AH shown in Table 3 are Examples of the present invention in which an alumina-graphitic refractory was used as the corrosion resistant refractory. The number of useful channels of the present invention is higher than that of 17 channels of the conventional example.
It was more than ch.

In Examples A to C, the corrosion resistant refractory to be buried has the same graphite content, the thickness t1 is gradually decreased, and the thicknesses t2 and t3 of the spall resistant refractory surrounding the periphery are increased. Is.

From these data, if the spall problem at the early stage of casting is avoided by the spall resistant refractory on the surface layer, it is possible to reduce the subsequent melting loss with the corrosion resistant refractory embedded inside, and the number of durable channels (nozzle) It is understood that the life) is extended.

Example D has the same conditions (graphite content, thickness t1) as the corrosion resistant refractory embedded in the inside, but the spall resistant refractory thickness t3 on the nozzle inner hole side where the melt loss is particularly severe is the same as Example B.
Is made thinner so that the corrosion-resistant refractory inside is exposed earlier than the outside of the nozzle.
The h number was obtained.

In Examples A, E, G, and H, and in Examples C and F, the thickness conditions t1, t2, and t3 of each refractory were the same, but the graphite content of the corrosion-resistant refractory was changed. It can be seen that the lower the graphite content, the higher the corrosion resistance and the longer the number of useful channels.

Examples IK are alumina as a corrosion resistant refractory.
It is an example of the present invention using zirconium boride-graphite and zirconium boride-graphite refractory. The thickness t1, t2, t3 of each refractory is similar to Examples A, E, G, H,
Corrosion resistance Since the refractory composition is different, the results of the erosion test are excellent as shown in Table 2, and the number of durable channels is Examples A, E,
It shows a value higher than G and H.

Comparative Examples LR shown in Table 4 are Comparative Examples of the present invention in which an alumina-graphitic refractory was used as the corrosion resistant refractory.

In Comparative Examples L and N, the thickness t1 of the corrosion-resistant refractory to be buried is too large, and the thickness t of the spall-resistant refractory in the surface layer is t.
Since 2 and t3 were the lower limit value of 5 mm or less, a spalling problem in the initial stage of casting occurred and the number of useful ch was extremely short.

Further, in Comparative Examples M and O, the thickness t1 of the corrosion-resistant refractory to be buried is too thin and the lower limit value is 3 mm or less, so that the structure is a triple structure, but in the actual structure, the spall resistant material is almost the slag line portion. Therefore, there is no great difference from the conventional material, and the number of durable channels is comparable to that of the conventional material.

In Comparative Examples P and Q, the ratio of the graphite content exceeds the upper limit of the invention, and the graphite content is the same as that of the conventional spall-resistant refractory, so that the durability ch number was comparable to that of the conventional material. In Comparative Example R, the ratio of the graphite content was below the lower limit of the invention, and the spall resistance of the corrosion resistant refractory was remarkably reduced, so that the life was only 1 ch.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

Next, an example of the immersion nozzle will be described. Tables 5 to 8 show Examples and Comparative Examples of the present invention applied to the immersion nozzle.

FIG. 4 shows a sectional image diagram of the immersion nozzles of the embodiment of the present invention and a comparative example, and FIG. 5 shows a sectional image diagram of the immersion nozzle of the conventional example. In FIGS. 4 and 5, 1 is a high heat resistant spalling material, 2 is a high corrosion resistant material (embedding material), and 3 is a high heat resistant spalling material (for immersion nozzle slag line).

Tables 5 and 6 show the components of the spall resistant refractory and the corrosion resistant refractory used in the examples and the results of the rotary erosion test. The rotary erosion test was performed as described above. The spoma resistant refractory used in the rotary erosion test is, as shown in Table 5,
A zirconia-graphitic refractory (scaly graphite: 25% by weight, zirconia: 75% by weight) used in the slag line portion of the conventional structure nozzle was used.

As shown in Table 6, nine types of corrosion-resistant refractory materials to be buried are listed for each component, but the following three types are basic systems. Table 6 is based on the composition used for the long nozzle shown in Table 2 and has the content of replacing the alumina component with the zirconia component. -Zirconia-graphite refractory: (1), (2),
(3), (4), (8), (9) -Zirconia-zirconium boride-graphite refractory:
(5) ・ Zirconium boride-graphite refractory: (6), (7)

Table 7 shows the practical data of the examples of the present invention.
Contents of combination of corrosion resistant refractory and spall resistant refractory,
The thickness t1, t2, t3 of each refractory and the obtained service c
The h number is shown. Similar to Table 7, Table 8 shows the actual data of Comparative Example and Conventional Example. The conditions shown in Tables 7 and 8 were the same as those used for the evaluation of the long nozzle. As can be seen from Tables 7 and 8, also with respect to the immersion nozzle, the nozzle to which the present invention was applied similarly to the long nozzle showed higher durability than the conventional nozzle.

[0048]

[Table 5]

[0049]

[Table 6]

[0050]

[Table 7]

[0051]

[Table 8]

[0052]

According to the present invention, the corrosion resistance and spall resistance of the refractory material in the nozzle slag line portion are improved, and the durability of the nozzle can be greatly improved. In addition, it is possible to omit post-forming finishing cutting of a highly corrosion-resistant material that requires cutting, and it is possible to economically use because expensive materials are not scrapped. Furthermore, even materials that have not been used conventionally and have poor heat-resistant spalling properties can be used without deteriorating the heat-resistant spalling properties of the entire slag line portion, and the range of material selection is expanded.

[Brief description of drawings]

FIG. 1 (a) is a sectional view of a slag line portion A of a nozzle to which the present invention is applied. (B) X of the slag line portion A of the nozzle to which the present invention is applied
It is a -X 'sectional view.

FIG. 2 is a vertical sectional view of a long nozzle according to an embodiment of the present invention.

FIG. 3 is a vertical cross-sectional view of a conventional long nozzle.

FIG. 4 is a vertical sectional view of an immersion nozzle according to an embodiment of the present invention.

FIG. 5 is a vertical sectional view of a conventional immersion nozzle.

[Explanation of symbols]

1 High heat resistance spalling material 2 High corrosion resistance material (embedding material) 3 High heat resistance spalling material (for immersion nozzle slag line)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location B22D 41/54 C04B 35/00 (72) Inventor Seiji Hanagiri 1st Nishinosu, Oita City, Oita Prefecture New Nippon Steel Co., Ltd. Oita Works (72) Inventor Yoshitaka Hiraiwa 1-1 Higashihama-cho, Hachimansai-ku, Kitakyushu, Fukuoka Prefecture Kurosaki Ceramics Co., Ltd. (72) Koji Ogata 1-Higashihama-cho, Hachimansai-ku, Kitakyushu, Fukuoka 1- 1 Kurosaki Ceramics Co., Ltd. (72) Inventor Yoichi Yokoyama 1-3-1 Niihama, Arai-cho, Takasago-shi, Hyogo Harima Ceramic Co., Ltd. (72) Masami Nishikawa 1-3-1 Niihama, Arai-cho, Takasago-shi, Hyogo Hari Inside of Macceramic Co., Ltd.

Claims (4)

[Claims] 1. A refractory structure at a portion where a continuous casting nozzle contacts a molten metal meniscus portion, wherein inner and outer walls of the nozzle are spall resistant refractory layers, and an intermediate portion thereof is a corrosion resistant refractory layer. Nozzle for continuous casting. 2. The refractory forming the spall resistant refractory layer is an alumina-graphitic refractory or zirconia-graphite refractory containing 20-30 wt% of scaly graphite, and the corrosion resistant refractory layer is In the corrosion resistance test conducted under the same conditions, the refractory to be constituted shows a melt loss index of 80 or less when the melt loss index of the refractory constituting the spall resistant refractory layer is 100. The continuous casting nozzle according to claim 1. 3. The continuous casting according to claim 1, wherein the refractory forming the corrosion-resistant refractory layer is any one of the following refractories containing 1-15% by weight of scaly graphite. nozzle. Alumina-graphite refractory Alumina-zirconium boride-graphite refractory Zirconium boride-graphite refractory Zirconia-graphite refractory Zirconia-zirconium boride-graphite refractory 4. The thickness relationship between the spall resistant refractory layer of the inner and outer walls of the nozzle and the corrosion resistant refractory layer of the middle portion is T in the radial direction from the inner surface of the nozzle to the outer surface of the nozzle,
The thickness of the corrosion-resistant refractory layer in the middle part is t1, the thickness of the spall-resistant refractory from the nozzle outer wall surface side to the middle part of the corrosion-resistant refractory layer is t2, and the corrosion-resistant refractory layer surface in the middle of the nozzle inner hole surface Of spall resistant refractories up to t3
The nozzle for continuous casting according to any one of claims 1 to 3, characterized in that the relationship of the following formula (1) is satisfied.