JPH10137910A - Continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the temp. drop of molten steel caused by heat radiation in a tundish and to realize a stable operation by blowing non-reactive gas of at least one kind of preheated inert gas or reducing combination exhaust gas into the tundish at the initial stage and/or the end stage of casting. SOLUTION: The molten steel 17 is poured into the tundish 11 through a long nozzle 15 in a ladle 13. The non-active gas is blown into the tundish 11 and recovered. For this purpose, pipings 23, 24 are inserted into opening holes of a roof 14. One end parts of the pipings 23, 24 are connected to a heat exchanger 25. The preheated inert gas or reduced combustion exhaust gas is blown into the tundish 11 from the piping 23 at the initial stage and/or at the necessary time in the end stage and the gas is recovered through the piping 24 and heat-exchanged with the blowing gas by using the heat exchanger 25. By this method, the clogging of the nozzle and the sticking of the molten steel, etc., to the inner wall of the tundish can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a stable operation of a continuous casting of molten steel by preventing the temperature of the molten steel from decreasing due to heat radiation of the tundish even when the amount of the molten steel in the tundish becomes smaller than a steady level. To a continuous casting method that enables

[0002]

2. Description of the Related Art In general, when continuously casting molten steel, the temperature of the molten steel in a tundish, which is an intermediate vessel between a ladle and a mold, is raised by 10 to 25 ° C. from the liquidus temperature. By applying the composition, a sound solidified shell is formed in the mold and the cast slab is cleaned, and the entire molten steel is cast in a normal state. However, since the amount of superheat is set based on the amount of molten steel during steady operation, the amount of molten steel in the tundish is lower than the steady level at the initial casting or at the end of casting, or at the ladle replacement period of continuous casting, The amount of heat cannot be compensated for a decrease in the temperature of the molten steel due to the radiation of the tundish, and the molten steel (including slag) tends to solidify. For this reason, after completion of casting, it is necessary to perform a troublesome operation such as a process of removing metal or slag adhering to the inner wall of the tundish. In particular, when the tundish is reused hot, even if it is attempted to discharge the metal or slag remaining in the tundish, the tundish adheres to the inside and cannot be completely discharged. As a result, when ingots and slag are attached to the tundish and the casting of new molten steel is started,
Ingots and slag are melted, diffused and mixed in this new molten steel, and the composition of the preceding slab and the following slab cannot be set to the required composition, the slab quality is reduced, The casting operation is hindered, for example, the yield decreases. Therefore, as a method of heating molten steel in a tundish,
A method of providing a burner in a tundish, for example, Japanese Patent Application Laid-Open Nos. 3-243254 and 6-114511
Patent Document 1: A method of providing a plasma torch on a tundish as disclosed in Japanese Patent Application Laid-Open No. 58-148057, and a method of providing an electromagnetic induction heating device on a tundish as disclosed in Japanese Patent Application Laid-Open No. 6-238405. Etc. have been proposed.

[0003]

However, in the above-mentioned method, since oxygen for burning the flame is required, the oxidation of the molten steel is remarkable. Even if molten steel can be discharged, oxides with a low melting point adhere and remain inside, so when starting the casting of new molten steel, the oxide melts, diffuses, and mixes in this new molten steel, and the quality of slabs Is reduced. When the flame is reduced to prevent the generation of oxides, as described above, ingots and slag adhere to the tundish, and when the casting of new molten steel is started, the ingot and slag are added to the new molten steel. However, there is a problem that the quality of cast slabs deteriorates due to melting, diffusion and mixing.
Further, the above method is effective when the amount of molten steel in the tundish is close to a steady level, but when the amount of molten steel in the tundish is small, it becomes difficult for the thermal energy of plasma to reach the molten steel. However, there is a problem that the heating efficiency becomes worse. Therefore, it is conceivable to provide a plasma torch that can move up and down on the tundish to follow the decreasing molten steel.In this case, when the amount of molten steel in the tundish decreases, the plasma directly hits the refractory. However, there is a problem of erosion. Therefore,
It becomes difficult to heat the molten steel in the tundish,
In the same manner as described above, the metal and slag remain, and the above-described problem occurs. In addition, in the above method, similarly to the above, although effective when the amount of molten steel in the tundish is close to the steady level, there is a problem that when the amount of molten steel in the tundish is small, the heating efficiency of the molten steel is deteriorated. Therefore, it is difficult to solve the problem caused by the slag and slag remaining in the tundish. The present invention has been made in view of such circumstances, and even when the amount of molten steel in a tundish becomes smaller than a steady level, it is possible to prevent the temperature of the molten steel from decreasing due to heat radiation of the tundish, thereby enabling stable operation. It is an object of the present invention to provide a continuous casting method.

[0004]

According to the present invention, there is provided a semiconductor device comprising:
The described continuous casting method is a continuous casting method for continuously casting molten steel, wherein at least one non-reactive gas of a preheated inert gas or a reducing combustion exhaust gas is tanned at the beginning of casting and / or at the end of casting. Blow into the dish. Claim 2
The continuous casting method according to claim 1, wherein the temperature of the preheated non-reactive gas blown into the tundish according to the ambient temperature and / or the amount of molten steel in the tundish in the continuous casting method according to claim 1. And / or controlling the flow rate to keep the ambient temperature in the tundish constant. The continuous casting method according to claim 3 is the continuous casting method according to claim 1, wherein the preheated non-reactive material blown into the tundish according to an ambient temperature and / or a quantity of molten steel in the tundish. The temperature and / or flow rate of the gas is controlled to maintain the temperature of the molten steel in the tundish within a certain range. A continuous casting method according to a fourth aspect of the present invention is the continuous casting method according to any one of the first to third aspects, wherein when the molten steel is continuously cast, the inside of the tundish is placed at the last stage of the previous continuous casting. From the time when the amount of molten steel starts to decrease below the steady level, and until the amount of molten steel in the tundish reaches the steady level in the early stage of the next continuous casting, the non-reactive gas preheated in the tundish. Blow in. In the early stage of continuous casting, at least the amount of molten steel in the tundish decreases from the steady level until the molten steel amount in the tundish starts to increase to a steady level at the end of continuous casting. From the start to the end of casting, a preheated non-reactive exhaust gas may be blown into the tundish. In the continuous casting method according to a fifth aspect, in the continuous casting method according to any one of the first to fourth aspects, after recovering the non-reactive gas blown into the tundish, preheating is performed again. Into the tundish.

[0005] Here, the initial stage of casting refers to a period from when the amount of molten steel in the tundish starts to increase until it reaches a steady level, and the end of casting refers to a period when at least the amount of molten steel in the tundish is constant. This is the period from when the level begins to decrease to the level at which casting ends. Also,
The non-reactive gas refers to an inert gas such as Ar gas, or a reducing combustion exhaust gas, or a mixture of both. The reducing combustion exhaust gas refers to a combustion exhaust gas generated when a gas fuel such as liquefied petroleum gas (LPG), coke oven gas (COG), or blast furnace gas (BFG) is burned at an air ratio of 1 or less. Preferably, the non-reactive gas is preheated to a temperature higher than the liquidus temperature of the molten steel. This is because, when the preheating temperature of the non-reactive gas is lower than the liquidus temperature of the molten steel, the temperature of the molten steel due to the radiation of the tundish is rather accelerated. It should be noted that although it depends on the amount of superheat of the molten steel and the flow rate of the non-reactive gas, the temperature is 5 to 30 ° C. higher than the liquidus temperature (T _L ) of the molten steel, preferably 8 ° C. It is preferable to set the temperature to ２５25 ° C. higher.

This is because the temperature of the non-reactive gas is (T _L +8)
℃) below, tend to promote the temperature drop of molten steel due to the heat radiation of the tundish rather than the above,
In particular, when the temperature is lower than ( _TL + 5 ° C), the tendency becomes remarkable. Conversely, when the temperature is higher than ( _TL + 25 ° C), the atmosphere temperature in the tundish becomes too high, and the refractory material is damaged by melting. At the same time, it becomes difficult to raise the temperature of the non-reactive gas and the cost tends to increase, and especially when the temperature exceeds ( _TL + 30 ° C.), the tendency becomes remarkable. The steady level refers to the optimum amount of molten steel in the tundish determined by casting conditions such as casting speed (see the broken line in FIG. 1). Further, the certain range is not particularly limited as long as the problem of temperature drop (particularly solidification) of molten steel due to heat radiation of the tundish can be eliminated, and may be appropriately selected according to the type of steel, casting conditions, and the like. Examples of the means for heating the non-reactive gas include a discharge heater and an electric heater. Furthermore, the non-reactive gas, for example, while being heated using the heating means while being supplied from a supply means such as a cylinder,
The gas may be supplied to the tundish, but in particular, since the inert gas is also an expensive gas, if it is allowed to leak from the tundish, the production cost increases. After recovering part or all, it is preferable to preheat again and blow it into the tundish.

Therefore, in the continuous casting method according to the first to fifth aspects, the amount of molten steel in the tundish is reduced, and the temperature of the molten steel is greatly reduced due to heat radiation of the tundish. During the ladle replacement period, the preheated non-reactive gas is blown into the tundish, so that the amount of heat can be compensated for the temperature drop of the molten steel, etc. It is possible to prevent clogging and adherence to the inner wall of the tundish, and it is possible to eliminate the need for a slab removal operation after completion of casting. Further, even if some molten steel or slag remains in the tundish, it does not solidify, so that it can be easily discharged when the tundish is hot-reused during the ladle exchange period of continuous casting. Therefore, to prevent the quality of cast slabs,
High quality slabs can be produced with high yield.
In particular, in the continuous casting method according to claims 2 and 3, for example, when a certain amount of non-reactive gas preheated to an appropriate temperature is blown into the tundish, if the amount of molten steel in the tundish is small, the It is not possible to prevent the temperature of the molten steel from dropping due to the heat radiation of the dish,
When the amount of molten steel in the tundish and the ambient temperature decrease, the inert atmosphere in the tundish is hindered.As a result, for example, external air may flow in and the molten steel may be oxidized. Can be prevented. Conversely, if the amount of molten steel in the tundish is large (for example, when the amount of molten steel is close to a steady level), the ambient temperature in the tundish becomes high, causing refractory erosion and / or in the tundish. There is a risk that the production cost will increase due to excessive supply of non-reactive gas more than necessary,
This can be prevented.

[0008] In the continuous casting method according to claim 4,
During continuous casting of molten steel, the amount of molten steel in the tundish starts to decrease from the steady level at the end of the previous continuous casting until the molten steel amount reaches the steady level in the early stage of the next continuous casting. By blowing a non-reactive gas into the dish, even at the beginning of casting or at the end of casting, for example, when the amount of molten steel in the tundish is at or near a steady level, a heat amount equal to or more than a predetermined amount of superheat is applied. As a result, similarly to the above, as described above, there is a possibility that the production cost due to the erosion of the refractory or the excessive supply of the non-reactive gas may increase, but by preventing this, it is possible to implement a cheap and stable casting operation. it can. In the continuous casting method according to claim 5, even if the canopy is covered, a completely sealed state cannot be formed, so it is necessary to supply an extra amount in consideration of leakage of the non-reactive gas. If the supply is excessive, the production cost rises and the atmosphere temperature in the tundish becomes high, and the refractory may be melted down as described above. However, the non-reactive gas once blown into the tundish After re-collecting, it is preheated again and blown into the tundish, so that it is possible to prevent an increase in production cost due to waste of an expensive inert gas, erosion of refractories, etc. It is possible to carry out a stable casting operation.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. Note that the same reference numerals are given to the same components in each embodiment, and the description will be omitted. (First Embodiment) First, a configuration of a continuous casting machine A that can be suitably used in a continuous casting method according to a first embodiment of the present invention will be described with reference to FIG. A ladle turret is provided on a cast floor of a building (not shown), and a ladle 13 is supported on a swing arm of the ladle turret. A traveling vehicle (not shown) is movably disposed on the casting bed below the ladle turret. The tundish 1 is placed on the traveling vehicle via a load cell (not shown).
1 is placed. Further, two oscillation devices (not shown) are provided on the floor of the building described above, and a mold 12 is provided at the end of an arm of each oscillation device so as to be able to move up and down. And
Below each mold 12, a casting strand (not shown) for supporting a slab (not shown) drawn from the mold 12 is provided.

Next, a specific configuration of the above-described continuous casting machine A will be described in detail with reference to FIG. As shown in the drawing, a canopy 14 is placed on the upper surface of the boat-shaped tundish 11 to make the inside of the tundish 11 almost in a sealed state. At the center of the canopy 14 is a tap 13 provided at the center of the bottom of the ladle 13.
An insertion port 14a for inserting the long nozzle 15 communicated with a is provided. Further, two tap holes 11a are opened at the bottom of the tundish 11, and a dipping nozzle 16 for pouring molten steel 17 into each mold 12 is attached to each tap hole 11a. . Further, the lower surface of the canopy 14 and the lower surface of the tundish 11 are poured from a ladle 13 to prevent molten metal 17 from being mixed with molten steel 17 poured into each mold 12. A pair of weirs 19 and 20 are provided, respectively.

In FIG. 1, reference numeral 21 denotes molten steel 17 accumulated between a pair of weirs 20 in the tundish 11 at the end of casting.
This is a discharge port for discharging the slag 18 and a flap 22 which can be freely opened and closed.
The continuous casting machine A is an example of a non-reactive gas supplied from a cylinder (not shown) into the tundish 11.
The pipe 23 is inserted into an opening (not shown) formed in the canopy 14 for blowing r gas, and the Ar gas blown into the tundish 11 and heating the molten steel 17 is recovered by the canopy 14. And a pipe 24 inserted into the opened hole (not shown).
One end of 4 is connected to the heat exchanger 25. Reference numeral 26 denotes an adjustable valve attached to the pipe 23, which receives a control signal from the tundish 11 and a control unit (not shown) that detects an output signal of a load cell for measuring the amount of molten steel in the tundish 11. Thus, Ar gas can be supplied at a flow rate corresponding to the amount of molten steel in the tundish 11.

Next, with reference to FIGS. 1 and 2, a description will be given of a continuous casting method according to the present embodiment for continuously casting molten steel of different steel types using the continuous casting machine A having the above-described configuration. First, the molten steel 17 is poured into the tundish 11 by adjusting the sliding nozzle 29 of the long nozzle 15 of the ladle 13. In the present embodiment, low-carbon steel having a liquidus temperature T _L = 1530 to 1550 ° C. is used, and casting is performed in a state where a superheat amount of 10 to 25 ° C. is applied thereto. When the molten steel 17 has accumulated about half in the tundish 11, each immersion nozzle 1
The molten steel 17 is poured into each mold 12 by adjusting the stopper nozzle 6 (not shown). Next, the amount of molten steel in the tundish 11 is reduced to a steady level L indicated by a broken line in FIG.
_When reaching ₁ , the sliding nozzle 29 of the long nozzle 15 is throttled. In this case, in consideration of the amount of molten steel is poured into the mold 12, always shall be held steady level L ₁ of the amount of molten steel in the tundish 11. Then, the casting operation is continued while the amount of molten steel in the tundish 11 is kept at a constant level (in the present embodiment, the casting speed is 1.
When the molten steel in the ladle 13 has been poured into the tundish 11 (time t _{0 in} FIG. 2), a swing arm (not shown) is moved, and new molten steel is placed on the tundish 11. Bring the ladle 13 to be stored.

Further, when the molten steel in the ladle 13 has been poured into the tundish 11 and the amount of molten steel in the tundish 11 starts to drop below the steady level L ₁ (time t _{0 in} FIG. 2), The casting speed is gradually reduced, and a constant temperature (T ₄ in FIG. 2B) is maintained in the tundish 11.
(C) starts to supply the preheated Ar gas. In the present embodiment, the preheating temperature T ₄ of the Ar gas is set to a temperature higher by 8 to 25 ° C. than the liquidus temperature of the molten steel 17. In addition, the flow rate of Ar gas is also increased in accordance with the rate of decrease in the amount of molten steel in the tundish 11 (see FIG. 2B). And the amount of molten steel in the tundish 11 is 3 to 1 T (ton).
When the value becomes less than (at time t ₁ in FIG. 2A), A
The flow rate of the r gas was kept constant (in FIG. 2B, V ₂ m ³ /
Minutes), adjust the sliding nozzle 29 of the long nozzle 15 of the new ladle 13 and start pouring new molten steel into the tundish 11. At this time, tundish 11
When the molten steel amount of inner began increased (see FIG. 2 (b)) (in FIG. 2, t ₂ hours) than, the flow rate of Ar gas also reduces in accordance with the increasing speed of the amount of molten steel. In addition, since the preheated Ar gas is supplied into the tundish 11, the temperature of the molten steel 17 in the tundish 11 is reduced to a lower limit by preventing a decrease in the ambient temperature in the tundish 11. It is possible to prevent the temperature from dropping below the temperature (T ₁ degrees in FIG. 2C), and to prevent the occurrence of residual slag or residual slag in the tundish 11 which hinders the quality of the next charge. When the amount of molten steel in the tundish 11 has reached a steady-state level L ₁ (FIG. 2 (a), the in (b), t ₃
Time), the supply of Ar gas is stopped (see FIG. 2B). Incidentally, the molten steel temperature in the tundish 11, (in FIG. 2 (c), t ₄ hours) before the amount of molten steel in the tundish 11 to reach steady-state level L ₁ reaches a temperature T ₂ of the required upper limit on.

As described above, the continuous casting method according to the present embodiment has the following advantages. That is, conventionally,
The ladle exchange phase of communicating continuous casting of molten steel of the tundish 11 is less than the steady-state level L _1, tundish 11
The amount of heat could not be compensated for the temperature drop of the molten steel 17 due to the intense heat radiation, and the molten steel 17 was easily solidified. However, the Ar gas preheated to a temperature higher than the liquidus temperature of the molten steel 17 was transferred into the tundish 11. Into the molten steel 1
Because the amount of heat can be compensated for the heat radiation of 7,
It is possible to prevent the temperature of the molten steel 17 from dropping, thereby preventing nozzle clogging of the molten steel 17 and the like and adhesion to the inner wall of the tundish 11. As a result, it is possible to avoid the adhesion of the ingot or slag to the inner wall of the tundish 11 and the oxidation of the ingot, prevent the quality of the slab from being reduced, and produce a high-quality slab with a high yield. it can. Further, for example, when a fixed amount of preheated Ar gas is simply blown into the tundish 11, if the amount of molten steel in the tundish 11 is small, the temperature of the molten steel 17 due to the heat radiation of the tundish 11 decreases, The oxidation of the molten steel 17 due to the inhibition of the internal inert atmosphere cannot be prevented.
If the amount of molten steel in the tundish 11 is large, the temperature of the atmosphere in the tundish 11 may be increased, which may cause a problem such as damage to refractories.

However, the flow rate of Ar gas is controlled in accordance with the amount of molten steel in the tundish 11 so that the tundish 11
2C is maintained within a certain range (refer to the symbol ΔT in FIG. 2C; however, in the present embodiment, ΔT = T ₂ −T ₁ = 20 ° C.), so that the above-described problem is solved. be able to. Also, for example, when the preheated Ar gas is unilaterally supplied into the tundish 11, for example, the canopy 1
4 cannot form a completely sealed state, and the Ar gas leaks more than necessary from the gap between the canopy 14 and the tundish 11, wasting expensive Ar gas, thereby reducing manufacturing costs. In addition to the possibility of soaring, the inside of the tundish 11 may be heated to a high temperature, and the refractory may be damaged by melting, as described above. However, by recovering the Ar gas blown into the tundish 11 and then blowing it back into the tundish 11, the above-described problem can be solved.

(Second Embodiment) Next, a continuous casting method according to a second embodiment of the present invention will be described with reference to FIGS. In addition, the continuous casting machine A that can be preferably used in the continuous casting method according to the present embodiment is a continuous casting machine A that can be preferably used in the continuous casting method according to the first embodiment of the present invention. The description is omitted because it is similar. Next, the continuous casting machine A having the above configuration
The continuous casting method according to the present embodiment for continuously casting molten steel of a different steel type while hot-reusing the tundish 11 using the method will be described. First, casting of molten steel 17 is started in the same manner as in the first embodiment of the present invention. Then, the casting speed is gradually increased from when the molten steel 17 in the ladle 13 has been supplied into the tundish 11 and the amount of molten steel in the tundish 11 starts to decrease (time t ₀ in FIG. 3A). At the same time, the Ar gas preheated to a constant temperature (T ₄ ° C in FIG. 3B) is started to be supplied into the tundish 11.

Next, the amount of molten steel in the tundish 11 is 3
１1T (ton) (in FIG. 3 (a), t ₁
(Time), the casting speed is made substantially constant (about 0.1 m / min in the present embodiment), and the flow rate of Ar gas is made constant (V ₂ m ³ / min in FIG. 3B). And, note when it becomes hot water end (in Fig. 3 (a), t ₅ hours), squeeze the stopper nozzle of the tundish 11. Then, the traveling cart is run, the tundish 11 is transported to the dump site, the flap 22 is opened, and the molten steel 17 and slag remaining at the bottom of the tundish 11, that is, between the pair of weirs 20, are drained. The sliding nozzle 29 and the tundish 11 are repaired. At this time, tundish 11
The flow rate of the Ar gas is controlled in accordance with the amount of molten steel in the tundish, so that the atmosphere temperature in the tundish 11 due to the generation of residual slag and residual slag in the tundish 11 which hinders the quality of the next charge. In addition to preventing the temperature of the molten steel 17 from dropping below the lower limit temperature T ₁ ° C, not only can the molten steel and slag be sufficiently removed, even if the molten steel remains in the tundish 11, The oxidation of the residual molten steel can be prevented.

Then, the traveling carriage is caused to travel on the mold 12, and the swing arm is moved in advance to
Adjust the sliding nozzle 29 of the long nozzle 15 of the new ladle 13
Start pouring new molten steel in 1. At this time, when the amount of molten steel in the tundish 11 starts to increase (in FIG. 3A,
t ₆ hours), the Ar
The gas flow rate is also reduced (see FIG. 3B). And
When the molten steel amount in the tundish 11 has reached a steady-state level L ₁ (in FIG. 3 (a), t ₇ hours) to stop the supply of the Ar gas (see Figure 3 (b)). In addition, tundish 1
The molten steel temperature in ₁ reaches the upper limit temperature T ₂ before the amount of molten steel in the tundish 11 reaches the steady level L ₁ (t ₈ hours in FIG. 3C). As described above, according to the continuous casting method according to the present embodiment, the first embodiment of the present invention can be performed even when the molten steel of a different steel type is continuously cast while the tundish 11 is hot reused. The same effect as in the embodiment can be obtained.

(Third Embodiment) Next, FIG.
(A) A continuous casting method according to a third embodiment of the present invention will be described with reference to FIGS. First, FIG.
The configuration of a continuous casting machine B that can be suitably used in the continuous casting method according to the present embodiment will be described with reference to FIG. As shown, the continuous casting machine B used in the continuous casting method according to the present embodiment is different from the continuous casting machine A used in the continuous casting method according to the first embodiment of the present invention, in that:
Opening 14b opened in canopy 14 of tundish 11
In addition, a temperature measuring probe 27 for measuring the atmosphere temperature in the tundish 11 is provided, and the temperature of the atmosphere in the tundish 11 measured by the temperature measuring probe 27 is detected. The point is that a control unit 28 for controlling the temperature of Ar gas by controlling an electric heater, which is an example of a heating unit (not shown), is provided.

Next, with reference to FIGS. 2 (a), 4 and 5, a continuous casting machine B having the above-described configuration is used to continuously cast molten steel of different steel types according to the present embodiment. The casting method will be described. First, casting of molten steel 17 is started in the same manner as in the first embodiment of the present invention. Then, the amount of molten steel in the tundish 11 starts to decrease (FIG. 2A,
Before the time t ₀ in FIG. 3 (a), a stage where a decrease in the temperature of molten steel in the tundish 11 due to a decrease in the amount of molten steel in the ladle 13 is detected (FIGS. 2 (c) and 3 (c)) )), The supply of the preheated Ar gas into the tundish 11 is started. At this time, the flow rate of the Ar gas is kept to a constant amount (in FIG. 5 (a), the reference numeral ^{_{V 3: V 3 = 2~4m 3}} /
Minute), the temperature of the Ar gas is increased in accordance with the rate of decrease in the temperature of the molten steel in the tundish 11 (FIG. 5 (a)).
reference). Further, T ₅ represents the temperature of the inert gas to flow to normal levels. Then, (in FIG. 2 (a), t ₀ h) amount of molten steel in the tundish 11 starts to decrease from the steady-state level L ₁ than time, the start gradually lowering the casting speed, further increasing the temperature of the Ar gas start.

Of course, here, too, the tundish 11
It is assumed that the temperature of the Ar gas is increased in accordance with the decreasing speed of the amount of molten steel therein (see FIG. 5A). The temperature of the Ar gas is kept constant from the time when the amount of molten steel in the tundish 11 becomes less than 3 to 1 T (ton) (time t _{1 in} FIG. 2A) (see FIG. 5A). reference numeral T _3: T ₃ = 154
0-1575 ° C). Next, when a new molten steel is poured from the new ladle 13 into the tundish 11 and the amount of molten steel in the tundish 11 starts to increase (FIG. 2A).
From the time t ₂ ), the temperature of the Ar gas is gradually lowered while keeping the flow rate of the Ar gas constant (see FIG. 5A). When the amount of molten steel in the tundish 11 has reached a steady-state level L ₁ (in FIG. 2 (a), t ₃ hours), A
The supply of the r gas is stopped (see FIG. 5A).

As described above, according to the continuous casting method of the present embodiment, the temperature of the Ar gas blown into the tundish 11 is controlled in accordance with the ambient temperature in the tundish 11, and the tundish is controlled. Even when the atmosphere temperature in the chamber 11 is kept constant (see FIG. 5B), the same effect as in the continuous casting method according to the first embodiment of the present invention can be obtained. Further, for example, FIG. 2 (c), the as shown in FIG. 3 (c), in the molten steel of the tundish 11 starts subtracted from steady-state level L ₁ (FIG. 2 (c), the FIG. 3 (c), the t ₀
Before the time), the temperature of the molten steel in the tundish 11 starts to decrease gradually, but the temperature of the Ar gas is controlled according to the temperature of the atmosphere in the tundish 11 so that the temperature of the atmosphere in the tundish 11 is kept constant. Because it was held in
Even if the heat radiation of the molten steel 17 based on the decrease in the amount of molten steel in the ladle 13 proceeds, the molten steel 1 based on the decrease in the amount of molten steel in the ladle 13
7 can be prevented from promoting heat radiation.

(Fourth Embodiment) Next, FIG.
A continuous casting method according to a fourth embodiment of the present invention will be described with reference to FIGS. The continuous casting machine B that can be suitably used in the continuous casting method according to the present embodiment is different from the continuous casting machine B that can be suitably used in the continuous casting method according to the third embodiment of the present invention. The description is omitted because it is similar. Next, a continuous casting method according to the present embodiment for continuously casting molten steel of a different steel type while hot-reusing the tundish 11 using the continuous caster B having the above-described configuration will be described. First, casting of molten steel 17 is started in the same manner as in the first embodiment of the present invention. Then, before the amount of molten steel in the tundish 11 begins to decrease (time t ₀ in FIGS. 2A and 3A), a stage in which a decrease in the temperature of the molten steel in the tundish 11 is detected (FIG. 2 ( c), see FIG. 3 (c)). The supply of the preheated Ar gas into the tundish 11 is started.

At this time, the temperature of the Ar gas is increased while the flow rate of the Ar gas is kept constant (V ₃ m ³ / min in FIG. 6A) (see FIG. 6A). Then, (in FIG. 3 (a), t ₀ h) amount of molten steel in the tundish 11 starts to decrease from the steady-state level L ₁ than time, the start gradually lowering the casting speed begins to increase the temperature of the Ar gas . Next, the amount of molten steel in the tundish 11 is 3 to 1T.
(Tons) made on the degree (in FIG. 3 (a), t ₁ hour) than when, for a constant temperature of the Ar gas (in FIG. 6 (a), T ₃
° C). Incidentally, T ₅ represents the temperature of the inert gas to flow to normal levels. And when pouring is completed (FIG. 3 (a)
(Middle, t ₅ hours), the stopper nozzle of the tundish 11 is squeezed, and the traveling cart is moved to the dumping place to discharge the molten steel 17 and the slag in the tundish 11 and to repair the sliding nozzle 29 and the tundish 11. I do.

Then, the traveling carriage is moved to the position above the mold 12, the sliding nozzle 29 of the long nozzle 15 of the new ladle 13 is adjusted, and new molten steel is poured into the tundish 11. At this time, tundish 1
From the time when the amount of molten steel within 1 starts increasing (time t ₆ in FIG. 3 (a)), the temperature of Ar gas is gradually increased in accordance with the increasing speed of the amount of molten steel while keeping the flow rate of Ar gas constant. (See FIG. 6A). And Tundish 1
1 when the amount of molten steel in steel ₁ has reached the steady level L ₁ (see FIG. 3).
In (a), to stop the supply of the Ar gas to t ₇ h) reference (FIG. 6 (a)). As described above, according to the continuous casting method according to the present embodiment, even when the molten steel of a different steel type is continuously cast while hot reusing the tundish 11, the atmospheric temperature in the tundish 11 is reduced. Accordingly, the temperature of the Ar gas blown into the tundish 11 is controlled,
Since the atmosphere temperature in the tundish 11 is kept constant (see FIG. 6B), the same effects as in the first and third embodiments of the present invention can be obtained.

[0026]

Next, the results of a confirmation test of the continuous casting method according to the first embodiment of the present invention will be described. Example 1 First, continuous casting of molten steel (liquidus temperature T _L = 1535 ° C.) of low carbon steel having a carbon concentration of 1 wt% or less at 1555 ° C. was performed. Then, when replacing the ladle, the amount of molten steel in the tundish is reduced from the steady level (40T) at the end of the previous continuous casting in the same manner as in the continuous casting method according to the first embodiment of the present invention. From the beginning of the process, until the molten steel amount reaches the steady level in the early stage of the next continuous casting, 1 is an example of a non-reactive gas in the tundish.
Ar gas at 555 ° C. was blown, and the flow rate of Ar gas was controlled in accordance with the amount of molten steel in the tundish to control the temperature of the molten steel in the tundish to be within a certain range (ΔT = 10 ° C.). (See FIGS. 7A, 7B, and 7D). The result is shown in FIG.

As a result, no adhesion of molten steel or slag in the tundish was observed at the end of the first continuous casting, and it was confirmed that a good casting operation could be performed. Also,
For example, when a fixed amount of pre-heated Ar gas is blown into the tundish, the volume of space in the tundish increases with a decrease in the amount of molten steel in the tundish, thereby providing a kind of draft effect to the tundish. Although there is a possibility that the air may appear and the invasion air from the outside may increase, FIG.
As shown in the figure, the O ₂ concentration in the tundish was confirmed to be constant, and the effect of preventing the oxidation of molten steel due to the intrusion of external air and the deterioration of the quality of the next continuous cast slab due to oxidation of the molten steel Was able to be prevented.

The embodiment of the present invention has been described above.
The present invention is not limited to the above-described embodiment, and all changes in conditions that do not depart from the gist are within the scope of the present invention. For example, in the first to fourth embodiments of the present invention, the Ar gas, which is an example of the non-reactive gas, is blown into the tundish 11, but another inert gas may be blown, or the reducing combustion exhaust gas may be blown. May be blown. In the first and second embodiments of the present invention, the flow rate of the Ar gas is controlled according to the amount of molten steel in the tundish 11. The temperature may be controlled (at a constant flow rate), or the temperature and flow rate of the inert gas may be controlled. Further, in the first and second embodiments of the present invention, the temperature of the molten steel in the tundish 11 is maintained within a certain range (refer to the symbol ΔT in FIG. 2C). The temperature may be kept constant. Further, in the third and fourth embodiments of the present invention, the temperature of the Ar gas is controlled according to the ambient temperature in the tundish 11. The flow rate may be controlled (at a constant temperature) or the temperature and flow rate of the inert gas may be controlled. In addition, in the third and fourth embodiments of the present invention, the atmosphere temperature in the tundish 11 is kept constant. However, as shown in FIG. (Refer to the symbol ΔT in FIG. 2C). In the third and fourth embodiments of the present invention, the tundish 11
Although the temperature of the Ar gas was controlled in accordance with the ambient temperature inside, the valve 26 of the pipe 23 was removed, but it may be left attached.

In the first to fourth embodiments of the present invention, the flow rate or temperature of the Ar gas is controlled according to the amount of molten steel in the tundish 11 or the ambient temperature. The flow rate or temperature of Ar gas, or both, may be controlled in accordance with the ambient temperature and the ambient temperature. Also,
In the first to fourth embodiments of the present invention, when the amount of molten steel in the tundish 11 began subtracted from steady-state level L ₁ (in FIG. 2 (a), t ₀ h), once the flow rate of the Ar gas 0 m ³ / min V ₁ m ³ / up to the minute (see FIG. 2 (b)), also when the amount of molten steel in the tundish 11 has reached a steady-state level L ₁ (in FIG. 2 (a), t ₃ hours ), Ar
The gas flow rate was reduced from V ₁ m ³ / min to 0 m ³ / min at a stretch (see FIG. 2B). But tundish 11
When the amount of molten steel in the tank begins to decrease below the steady level L ₁ (see FIG. 2)
In (a), from t ₀ hours), the molten steel of the tundish 11 (less than tons) (FIG. 2 (a) 3~1T in, t
₁ hour) and when the amount of molten steel in the tundish 11 starts to increase (time t ₂ in FIG. 2A), the amount of molten steel in the tundish 11 reaches the steady level L ₁ (FIG. 2). The flow rate of the Ar gas may be gradually changed (in proportion to the amount of molten steel) until (time t _{3 in} (a)). In the first to fourth embodiments of the present invention, the ladle replacement period in continuous casting has been described. However, the present invention is applied to, for example, the initial stage of casting as shown in FIG. 8 and the final stage of casting as shown in FIG. It is also possible.

[0030]

As is apparent from the above description, in the continuous casting method according to any one of the first to fifth aspects, the amount of molten steel in the tundish is reduced, and the temperature of the molten steel is greatly reduced due to the radiation of the tundish. Since the preheated non-reactive gas is blown into the tundish at the beginning of casting and / or at the end of casting, the amount of heat with respect to the heat radiation of molten steel or the like can be compensated, and the temperature of the molten steel or the like can be prevented from lowering. This can prevent clogging of the nozzle of the molten steel or the like and adhesion to the inner wall of the tundish, and furthermore, after completion of casting, the work of removing the ingot of the tundish can be omitted. In addition, in particular, in continuous casting, it is possible to avoid the worst situation in which hot reuse due to the adhesion of the tundish to the ingot becomes impossible. The slab can be produced with high yield. In particular, in the continuous casting method according to claims 2 and 3, for example, when the amount of molten steel in the tundish is reduced, it is possible to prevent the temperature of the molten steel from decreasing due to heat radiation of the tundish, and to reduce the temperature in the tundish. When the amount of molten steel is close to the steady level, it is possible to prevent the temperature of the atmosphere in the tundish from being increased, thereby preventing damage to the refractory.

[0031] In the continuous casting method according to the fourth aspect,
For example, even when the amount of molten steel in the tundish is close to the steady level, it is possible to prevent erosion of the refractory without applying a heat amount equal to or more than a predetermined overheat amount. In the continuous casting method according to the fifth aspect, for example, it is possible to prevent an unnecessary gas from leaking from a gap between the canopy and the tundish more than necessary and to increase the production cost, and to reduce the temperature of the atmosphere in the tundish. Can be prevented from becoming too hot and the refractory from being melted.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a continuous casting machine that can be suitably used in a continuous casting method according to first and second embodiments of the present invention.

FIG. 2 (a) is a characteristic diagram showing a change with time in the amount of molten steel in a tundish in the continuous casting method according to the first and third embodiments of the present invention. (B) and (c) are characteristic diagrams showing a temporal change of an inert gas flow rate and a temporal change of a molten steel temperature in a tundish, respectively, in the continuous casting method according to the first embodiment of the present invention.

FIG. 3 (a) is a characteristic diagram showing a change with time in the amount of molten steel in a tundish in a continuous casting method according to second and fourth embodiments of the present invention. (B) and (c) are characteristic diagrams respectively showing a temporal change of an inert gas flow rate and a temporal change of a molten steel temperature in a tundish in the continuous casting method according to the second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a continuous casting machine that can be suitably used in a continuous casting method according to third and fourth embodiments of the present invention.

FIGS. 5 (a) and 5 (b) are characteristic diagrams showing a temporal change of an inert gas temperature and a temporal change of a molten steel temperature in a tundish, respectively, in a continuous casting method according to a third embodiment of the present invention. .

FIGS. 6 (a) and 6 (b) are characteristic diagrams showing a temporal change of an inert gas temperature and a temporal change of a molten steel temperature in a tundish, respectively, in a continuous casting method according to a fourth embodiment of the present invention. .

FIGS. 7 (a) to 7 (d) respectively show changes over time in the amount of molten steel in the tundish, changes over time in the flow rate of the inert gas, and changes in the tundish in the example of the continuous casting method according to the first embodiment of the present invention. FIG. 3 is a characteristic diagram showing a change over time in the O ₂ concentration in the inside and a change in the temperature of molten steel in the tundish over time.

FIG. 8 is a characteristic diagram showing a change with time in the amount of molten steel in a tundish.

FIG. 9 is a characteristic diagram showing a change with time of the amount of molten steel in a tundish.

[Explanation of symbols]

A continuous casting machine B continuous casting machine L ₁ constant level t ₀ h t ₁ hour t ₂ h t ₃ h t ₄ h t ₅ h t ₆ h t ₇ h t ₈ hours 11 tundish 11a outflow 12 mold 13 ladle 13a tap hole 14 canopy 14a insertion port 14b opening 15 long nozzle 16 immersion nozzle 17 molten steel 18 slag 19 dam 20 dam 21 discharge port 22 flap 23 pipe 24 pipe 25 heat exchanger 26 valve 27 temperature measuring probe 28 control section 29 sliding nozzle

Claims (5)

[Claims] 1. A continuous casting method for continuously casting molten steel, wherein at least one non-reactive gas of a preheated inert gas or reducing combustion exhaust gas is introduced into a tundish at an early stage of casting and / or at a late stage of casting. Continuous casting method characterized by injecting into a continuous casting. 2. The tundish by controlling a temperature and / or a flow rate of the preheated non-reactive gas blown into the tundish according to an ambient temperature and / or a quantity of molten steel in the tundish. 2. The continuous casting method according to claim 1, wherein the atmosphere temperature in the inside is kept constant. 3. The tundish by controlling the temperature and / or flow rate of the preheated non-reactive gas blown into the tundish according to the ambient temperature and / or the amount of molten steel in the tundish. 2. The continuous casting method according to claim 1, wherein the temperature of the molten steel is maintained within a certain range. 4. When continuously casting the molten steel, from the time when the amount of molten steel in the tundish starts to decrease below a steady level at the end of casting of the previous continuous casting, at the beginning of casting of the next continuous casting. The continuous casting method according to any one of claims 1 to 3, wherein the preheated non-reactive gas is blown into the tundish until the amount of molten steel in the tundish reaches the steady level. 5. The continuous casting method according to claim 1, wherein the non-reactive gas blown into the tundish is recovered, and then preheated again and blown into the tundish. .