JP3364031B2 - Continuous casting method using tundish - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method using a tundish. More specifically, it relates to a continuous casting method using a tundish that can reduce the amount of molten steel deposited in the tundish when performing continuous casting.

[0002]

2. Description of the Related Art Recently, in a continuous casting method in which molten steel in a ladle is poured into a tundish, and the molten steel is poured into the mold from the tundish, the refractory cost of the tundish is reduced, heat loss and operation are reduced. For the purpose of reducing the number of personnel, after casting, the residual steel and residue of the tundish used for the casting are discharged as they are, hot maintenance is performed without cooling, and the tundish subjected to the hot maintenance is used. A continuous casting method for casting has been proposed (Japanese Patent Publication No. 5-26589).

The continuous casting method is a method in which the tundish can be repeatedly used after the completion of casting and in a state where the standby cooling time before the next casting is short.

However, for example, when a trouble occurs in the converter, the main body of the continuous casting machine, etc., and the tundish needs to be temporarily stopped, it is necessary to adjust the production time. When the work of the previous process such as the next refining process is stopped, the standby cooling time of the tundish becomes long, a large amount of molten steel in the tundish adheres, and the tundish is repeated. The problem is that it can be used very few times.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and the amount of molten steel deposited in the tundish is increased even when the waiting time of the tundish is long. It is an object of the present invention to provide a continuous casting method capable of reducing the amount of waste and prolonging the life of the tundish.

[0006]

The present invention is a continuous casting method in which molten steel from a ladle is poured into a tundish and the molten steel is poured from a tundish into a mold, which is repeated. It is expected that the surface temperature of the refractory of the tundish will be less than 1350 ° C when the casting is completed by injecting into the mold, the residual steel and the slag are discharged, and the casting is started again using the tundish. When the temperature of the refractory of the tundish is lower than 1100 ° C., the refractory of the tundish is controlled so that the surface temperature of the refractory at the start of casting becomes 1350 ° C. or higher. The present invention relates to a continuous casting method using a tundish characterized by heating in an oxidizing gas atmosphere.

[0007]

According to the method of the present invention, as described above, the molten steel from the ladle is poured into the tundish, the molten steel is poured into the mold from the tundish to finish the casting, and the residual steel and the residue are discharged. After slagging, when the surface temperature of the refractory of the tundish when starting casting again using the tundish is expected to be less than 1350 ° C., the surface temperature of the refractory of the tundish is 1100 ° C. Before the temperature falls below 13, the surface temperature of the refractory at the start of casting is 13
Continuous casting is carried out by heating the refractory of the tundish in a non-oxidizing gas atmosphere so that the temperature becomes 50 ° C. or higher.

According to the present invention, when the surface temperature of the refractory material of the tundish when the casting is started again using the tundish is expected to be less than 1350 ° C., the refractory material when the casting is started. One of the major characteristics is that it is heated so that the surface temperature becomes 1350 ° C. or higher.

When the casting is started again using the tundish, the surface temperature of the refractory of the tundish is 135
When the temperature is below 0 ° C, for example, when there is a problem with the converter, continuous machine, etc., and it must be repaired, and the tundish operation must be temporarily stopped, When the work of the previous process such as the secondary refining process is stopped for adjustment, two or more tundish are used together, one of them is used, while the other tundish is used. It may occur when waiting for.

As described above, when the surface temperature of the refractory of the tundish when the casting is started again using the tundish is expected to be less than 1350 ° C., the tundish of the tundish when starting the casting is expected. When the refractory is heated to a surface temperature of 1350 ° C. or higher, the amount of residual steel / slag adhering in the tundish is significantly reduced, and the effective capacity of the tundish is significantly reduced. can do.

[0011]

EXAMPLES A continuous casting method using the tundish of the present invention will be specifically described below.

First, molten steel from a ladle is poured into a tundish. At this time, normally, the tundish can be placed directly below the ladle, and the molten steel can be poured into the tundish by dropping the molten steel from the ladle.

Next, molten steel is poured into the desired mold from the tundish to complete the casting.

After the completion of casting, if necessary, the tundish is moved, for example, from above the mold to a position within the casting floor and near the mold, and then residual steel and residue are allowed to adhere to the tundish. To prevent, the residual steel and residue are drained from the tundish.

After the residual steel and the slag are removed from the tundish, if necessary, parts such as the immersion nozzle, the long nozzle and the stopper of the tundish are replaced, and the inner surface of the tundish is locally repaired. Hot maintenance may be performed.

Next, the molten steel from the ladle is poured again into the tundish, and the molten steel is poured into the mold from the tundish. Prior to that, when the surface temperature of the tundish refractory (wear brick) when pouring molten steel from the tundish into the mold is expected to be less than 1350 ° C., the surface of the tundish refractory Before the temperature falls below 1100 ° C., the tundish refractory is heated in a non-oxidizing gas atmosphere so that the surface temperature of the refractory at the start of casting becomes 1350 ° C. or higher.

When the molten steel is poured into the mold from the tundish, the surface temperature of the refractory of the tundish is 135.
The prediction of the temperature being lower than 0 ° C. can be made, for example, by the following method.

Molten steel from a ladle is poured into a tundish, and the molten steel is poured from a tundish into a mold.
One operation to remove the residual steel and the slag is called one cast. By repeating this operation, the time until the surface temperature of the refractory material of the tundish reaches 1350 ° C. or 1100 ° C. is examined in advance. The result looks like the graph shown in FIG.

The graph shown in FIG. 1 shows the regions I and II.
And area III.

When the elapsed time from the end of casting to the start of casting again using the tundish is within the range of region I after the tundish is operated with a predetermined number of casts, the refractory of the tundish is refractory. Surface temperature is 1
Since the temperature is 350 ° C. or higher, heating need not be performed.
Further, when the elapsed time is within the range of the area II,
Heating is performed so that the surface temperature of the refractory at the time of starting casting becomes 1350 ° C. or higher. Further, the elapsed time is the region III
When the temperature is within the range, the surface temperature of the refractory of the tundish falls below 1100 ° C., the joints of the refractory of the tundish may be opened, and local repair may be required. , The surface temperature of the refractory of the tundish is 1100 ° C or higher, that is, the region
When in the range of II, the refractory must be heated so that the surface temperature of the refractory at the start of casting is 1350 ° C or higher.

As described above, when the surface temperature of the refractory material of the tundish is lower than 1100 ° C., the refractory material causes joint openings and the like.
The refractory must be heated before the surface temperature of the tundish refractory falls below 1100 ° C.

The refractory of the tundish is heated in a non-oxidizing gas atmosphere. If such heating is carried out in an oxidizing gas atmosphere such as the air, not in a non-oxidizing gas atmosphere, the residual steel / slag adhering to the inner surface of the tundish is oxidized and the molten steel is removed from the ladle. When molten steel is poured into the tundish, the molten steel is contaminated. Typical examples of the non-oxidizing gas include nitrogen gas, argon gas, and helium. Among them, nitrogen gas is preferable because it is inexpensive.

As a method for heating the refractory of the tundish, for example, a radiant tube is inserted into the tundish and the refractory is heated using the radiant tube, or the refractory is directly heated by a reducing gas burner. A method of embedding a resistance heating element in a tundish refractory and heating the refractory by the resistance heating element, a method of heating the refractory by preheating the non-acidified gas atmosphere with plasma, and the like. can give. Among these methods, a method of inserting a radiant tube into a tundish and heating a refractory material using the radiant tube can make the tundish a closed system and prevent the inflow of external atmosphere gas. Therefore, it can be used particularly preferably in the present invention.

FIG. 2a is a schematic explanatory view showing an embodiment in which a radiant tube is inserted in the tundish.

A tundish cover 2 is placed on the tundish 1. The radiant tube 3 is inserted into the hole provided in the tundish cover 2, and the installation base 4 to which the radiant tube 3 is fixed is placed on the tundish cover 2. The lower surface of the tundish 1 is provided with tuyere 7 for mounting the immersion nozzle 5 shown in FIG. 2b. In this tuyere 7,
During the preheating, the blind nozzle 8 is attached to prevent the inflow of external atmosphere gas. During casting, as shown in Figure 2b,
The immersion nozzle 5 is attached, and molten steel is injected into the mold from the immersion nozzle 5. Also, the tundish 1 is provided with a gas introduction pipe 6,
By introducing a non-oxidizing gas into the tundish 1 from the gas introducing pipe 6, the internal atmosphere of the tundish 1 is made a non-oxidizing atmosphere.

The radiant tube 3 is, for example, a burner inserted in a sintered Si--C type ceramic tube whose one end is sealed, and heat generated during combustion of the burner is passed through the ceramic tube. And is used for propagating to the refractory in the tundish 1 and the internal atmosphere.

When the radiant tube 3 is used, since heat generation of about 6000 kcal / hr is possible per tube, the surface temperature of the refractory of the tundish 1 can be easily heated to 1350 ° C. or higher.

When the inside of the tundish 1 is heated by using the radiant tube 3 as described above, the inside of the tundish 1 is closed by closing the gap between the tundish 1 and the radiant tube 3 with the tundish cover 2. It can be a closed system.

The arrangement of the radiant tubes 3 is not particularly limited. For example, the radiant tubes 3 may be arranged at equal intervals in the central portion of the tundish 1 in the longitudinal direction in one to three rows. it can. Further, the number of the radiant tubes 3 is arbitrary as long as the surface temperature of the refractory material of the tundish 1 can be heated to a predetermined temperature and varies depending on the capacity of the tundish 1, etc., but is usually about 3 to 10. Is.

The surface temperature of the refractory of Tundish 1 is
For example, it can be obtained by measuring the temperature of the surface of the tundish 1 at a point equally divided into four in the longitudinal direction of the sidewall by means such as a thermocouple or a radiation thermometer, and measuring the average temperature.

As described above, when the surface temperature of the refractory of the tundish 1 when the casting is started again using the tundish 1 is expected to be less than 1350 ° C., the refractory of the tundish 1 is Surface temperature is 110
Before the temperature falls below 0 ° C., that is, within the range II of the graph shown in FIG. 1, heating is performed so that the surface temperature of the refractory at the start of casting becomes 1350 ° C. or higher. .

Thus, when heating is performed so that the surface temperature of the refractory material of the tundish 1 at the time of starting casting becomes 1350 ° C. or higher, the amount of molten steel deposited in the tundish 1 is significantly reduced. However, a decrease in the effective capacity of the tundish 1 can be significantly suppressed, and the life of the tundish 1 can be extended.

After completion of heating, the molten steel from the ladle may be poured into the tundish 1, and the molten steel may be poured into the mold from the tundish 1.

Next, the continuous casting method using the tundish of the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

Example 1 A tundish having a capacity of 25 t was used to adjust the surface temperature of the refractory of the tundish to the temperature shown in Table 1, and 100 t of molten steel at 1530 to 1570 ° C. was added to the tundish. After injecting the molten steel into the mold from the tundish, the amount of molten steel adhering to the inside of the tundish was measured. The results are also shown in Table 1 and shown in FIG.

[0036]

[Table 1]

From the results shown in Table 1 and FIG. 3, it can be seen that when the surface temperature of the refractory material is 1350 ° C. as a boundary, the amount of molten steel deposited in the tundish is significantly reduced at a temperature of 1350 ° C. or higher. .

Therefore, in the continuous casting method in which the tundish is repeatedly used, the surface temperature of the refractory of the tundish is set to 1 even during the intermittent operation in which the casting interval becomes long.
It can be seen that the amount of molten steel and slag attached can be significantly reduced by preheating to 350 ° C. or higher.

Example 2 A tundish having a capacity of 25 t was used, and after adjusting the surface temperature of the refractory of the tundish to about 1500 ° C., 100 t of molten steel at 1530 to 1570 ° C. was poured into the tundish. Then, the operation of injecting the molten steel into the mold from the tundish is 1 cast, 5 cast,
After performing 7 casts or 79 casts, the temporal change of the surface temperature of the refractory of the tundish when the tundish was left as it was was examined. The results are shown in Table 2 and FIG.

[0040]

[Table 2]

From the results shown in Table 2 and FIG. 4, the surface temperature of the refractory of the tundish decreases with the cooling time, but it changes depending on the number of times the tundish is used repeatedly (the number of casts), and It can be seen that the cooling rate decreases as it increases. It is estimated that this is because the heat storage of the refractory of the tundish progresses as the number of casts increases.

Therefore, since the cooling rate of the surface temperature of the refractory of the tundish varies depending on the number of times the tundish is repeatedly used, if the tundish is not used for casting for a while, the tundish is repeatedly used. By considering the number of times and paying attention to the cooling rate of the surface temperature of the refractory material of the tundish, the time when the surface temperature of the refractory material becomes less than 1100 ° C. can be estimated in advance.

Example 3 A tundish 1 shown in FIG. 2a was prepared. The maximum capacity of this tundish 1 was 25 t, and the required minimum tundish capacity was 18 t.

Using this tundish 1, the refractory of the tundish 1 was adjusted to have a surface temperature of 1350 ° C., and then molten steel at 1530 to 1570 ° C. was poured into the tundish 1 from a ladle. Next, as shown in FIG. 2b, after the immersion nozzle 5 is attached, the molten steel is poured into the mold from the immersion nozzle 5 of the tundish 1, and then the operation of discharging the residual steel and the residue as they are is repeated. Repeat casting until the capacity of dish 1 reaches the required minimum tundish capacity (18 t),
The number of casts was counted. This number of casts is called the tundish life.

It should be noted that the radiant tube 3 (sintered Si--C type ceramic tube, burner capacity: 36) was used after the residual steel and residue were discharged from the tundish 1 and before the molten steel was newly injected from the ladle. × 10 ⁴ kcal /
hr (air ratio 1.2), calorific value: 6000 kcal / h
The molten steel was heated by using 6 pieces of r), and the surface temperature of the refractory of the tundish 1 was adjusted to be always 1350 ° C. or higher. While heating, the gas introduction pipe 6
Nitrogen gas was introduced to adjust the atmosphere in the tundish 1 to always be a non-oxidizing atmosphere.

As a result, the tundish has a life of 12
It was 6 casts.

Comparative Example 1 In Example 3, the surface temperature of the refractory material of the tundish 1 was 1 after the residual steel and the slag were discharged from the tundish 1 and before the molten steel 18t was newly injected from the ladle.
The same operation as in Example 1 was carried out so that the surface temperature of the refractory material of the tundish 1 was always 1350 ° C. or higher, except that the operation of raising the temperature to 150 ° C. was included, and the life of the tundish 1 was examined.

As a result, the life of the tundish 1 is 1
It was 10 casts.

From the results of Example 3 and Comparative Example 1, the surface temperature of the refractory of Tundish 1 was measured during the period from the time when the residual steel and the slag were discharged from Tundish 1 and the molten steel was newly injected from the ladle. Is lower than 1350 ℃ by about 200 ℃ 1
It can be seen that the life of Tundish 1 is significantly reduced by 16 casts by only including 2 casts at 100 ° C.

[0050]

According to the continuous casting method of the present invention, the amount of molten steel adhered in the tundish can be reduced even when the standby cooling time of the tundish is long. The life of the dish can be extended.

Further, when two or more tundish are alternately used, if the method of the present invention is applied to the waiting tundish, the longevity of two or more tundish alternately used. Can be realized.

[Brief description of drawings]

FIG. 1 Surface temperature of refractory tundish is 1100
It is a graph which shows the relationship between the number of casts and the elapsed time at 0 ° C or 1350 ° C.

FIG. 2a is a schematic explanatory view showing an embodiment of a tundish having a radiant tube inserted therein, which is used in the present invention, and FIG. 2b is an immersion nozzle at a tuyere of the tundish shown in FIG. 2a. FIG. 7 is a partial schematic explanatory view showing one embodiment when the is attached.

FIG. 3 is a graph showing the relationship between the surface temperature of the refractory of the tundish and the amount of molten steel deposited in the tundish.

FIG. 4 1 cast, 5 casts, 7 casts or 7
It is a graph which shows the time-dependent change of the surface temperature of the refractory material of the tundish after 9 casts.

[Explanation of symbols]

1 tundish 3 radiant tubes

Front page continuation (72) Inventor Riichi Aoki 2-6-3 Otemachi, Chiyoda-ku, Tokyo Within Nippon Steel Corporation (72) Inventor Kentaro Fukushima 2-3-6 Otemachi, Chiyoda-ku, Tokyo (56) Reference JP-A-4-22567 (JP, A) JP-A-47-1456 (JP, A) JP-A-8-155599 (JP, A) JP-A-8- 159664 (JP, A) Actual development Sho 55-153484 (JP, U) Japanese Patent Publication 5-26589 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) B22D 11/10 310 B22D 41/005

Claims (2)

(57) [Claims] 1. A continuous casting method in which molten steel from a ladle is poured into a tundish, and the molten steel is poured from a tundish into a mold, which is repeated. When the tundish refractory surface temperature is expected to be less than 1350 ° C. when the casting is started again using the tundish after finishing and discharging the residual steel and the slag, the tundish The surface temperature of the refractory at the time of starting casting is 1350 before the surface temperature of the refractory of 1350 ° C. is lower than 1100 ° C.
A continuous casting method using a tundish, characterized in that the refractory material of the tundish is heated in a non-oxidizing gas atmosphere so that the temperature is at least ℃. 2. The continuous casting method using a tundish according to claim 1, wherein the refractory of the tundish is heated using a radiant tube.