JPH07227659A - Method for controlling cooling water of mold for continuous casting - Google Patents

Abstract

PURPOSE:To prevent the development of bleed, breakout, etc., caused by insufficient cooling by changing the casting speed at the unstable time, to suitably prevent the deformation of shell caused by excess cooling even in the case of the kind of steel having high solidified shrinkage ratio and to stably and safely execute the sequentially continuous casting after changing tundishes and the continuous casting of the different kinds of steels. CONSTITUTION:At the time of using DELTAT for difference between the temp. of cooling water supplied into a mold for continuous casting and the temp. of cooling water discharged, the cooling water quantity supplied to the mold is gradually reduced according to the lowering of the casting speed to gradually increase DELTAT. The supply of cooling water to the mold is controlled so as to gradually increase the cooling water quantity according to the increase of the casting speed to gradually reduce DELTAT.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an unsteady state of continuous casting (including when the casting is stopped) in which the casting speed is changed in the primary cooling of the continuous casting by stopping or starting the continuous casting or replacing the ladle. ), The cooling water control of the continuous casting mold that enables stable and safe production of high-quality continuous casting pieces without falling of the continuous casting pieces due to overcooling and bleeding due to insufficient cooling. Regarding the method.

[0002]

In continuous casting of slabs and the like, molten steel is poured from a ladle into an intermediate container generally called a tundish, and the molten steel is poured from a tundish into a continuous casting mold (hereinafter referred to as a mold), A continuous cast piece having a predetermined cross-sectional shape (hereinafter referred to as a continuous cast piece) is continuously drawn downward to solidify the core of the continuous cast piece, and then cut into a predetermined length. , Bloom and billet.

In such continuous casting, molten steel (continuous cast piece) is drawn from the mold and conveyed, and is solidified sequentially from the surface by the primary cooling in the mold and the secondary cooling in the secondary cooling zone. Generally, primary cooling is performed by water-cooling a mold that contacts molten steel (continuous cast piece) with cooling water, and secondary cooling is performed by transporting the continuous cast piece and spraying a water spray or the like. Therefore, the continuous casting equipment (hereinafter referred to as a continuous casting machine) has a machine length set so that the continuous cast pieces manufactured up to the machine end are completely solidified to the core, and the drawing speed, primary and secondary The cooling control controls the solidification rate.

By the way, when the continuous casting is stopped / finished by stopping the injection of molten steel into the mold, the top portion of the continuous cast piece (in the present invention, the top portion of the continuous cast piece is defined as It is necessary to surely solidify the bottom end portion of the continuous cast piece to be drawn out before the drawing. If the top of the continuous cast piece is not sufficiently solidified after the casting is stopped, the shell (solidified shell) formed on the surface of the continuous cast piece will break and bleeding of molten steel will occur. If such inconveniences occur, and in a serious case, a serious accident such as equipment damage or steam explosion may occur, which becomes a very serious problem in terms of equipment and safety.

Therefore, when stopping the injection of molten steel into the mold and ending the continuous casting in normal continuous casting,
At the end of casting, the casting speed is gradually reduced, and in an extreme case, the drawing is temporarily stopped, and the top of the continuous cast piece is sufficiently solidified, and then gradually drawn.

Further, continuous casting of different steel types is carried out,
When performing so-called continuous casting of different steel types (or continuous casting of the same steel type after tundish exchange), the casting speed is reduced and the casting is temporarily stopped after the casting of the previous steel type (the steel type that was cast earlier) is completed. It is common to start casting the next steel type after inserting a partition material (connecting jig) to separate the previous steel type and the next steel type (steel type that is subsequently cast) on the molten metal surface in the mold. is there.

That is, when casting different steel types one after another,
As shown in FIG. 3, after gradually reducing the casting speed, the casting was stopped to stop the casting, the tundish of the previous steel grade was moved, and then the partition material described above was inserted, and the tundish of the next steel grade was specified. The casting is started at the next time, the casting of the next steel type is started and the casting is restarted, and the casting speed is gradually increased to achieve continuous continuous casting. In FIG. 3, the M / D cooling water flow rate is the cooling water amount supplied to the mold, ΔT is the water temperature difference between the cooling water supplied to the mold and the cooling water discharged from the mold, and the T / D weight ratio. It is the weight ratio (%) of the tundish to the weight of the tundish during steady casting.

As a partitioning material used for continuous casting of different steel types, for example, a flat plate-shaped member disclosed in JP-B-49-42215 and a hollow block-shaped partitioning material disclosed in JP-A-54-142131. , And Japanese Patent Publication Sho 63-
Various types are known, such as the V-type partitioning material disclosed in Japanese Patent No. 15056.

However, in the case where such different steel grades are successively cast, if the previous grade is a steel grade having a high solidification shrinkage rate such as SUS304 steel, it is in contact with the mold when the casting speed is reduced and the casting is stopped. There is a problem that a cast piece (molten steel) largely contracts due to solidification, a so-called shell falls to the inside of the cast piece, a partition material cannot be inserted, or casting of the next steel type cannot be restarted. For example, SUS304 steel has a width a of 124
When 100 ton continuous casting was performed using a mold 50 (see FIG. 4) having a thickness of 0 mm and a thickness b of 200 mm, when the casting was stopped under the conditions of FIG. 3 described above, as conceptually shown in FIG. , The top of the continuous cast piece becomes tapered due to the shell falling, and 3 mm in the width direction (arrow c) and 12 mm and 10 mm in the thickness direction between the continuous cast piece 52 and the mold 50.
A gap (indicated by arrows d and e, respectively) is formed so that the slab support roll 54 can be seen from above the mold 50, and the injected molten steel flows downward as it is. Therefore, the molten steel can be injected again. It will be impossible.

As one of the causes of this, when the continuous cast piece is pulled out after the continuous casting is stopped and the solidification of the top portion of the continuous cast piece is insufficient, the above-mentioned problems such as bleeding occur. Fearfully, by overcooling the top of the continuous slab when the casting is stopped, the inside of the shell (inside the slab)
It can be mentioned that the collapse into

[0011]

The conventional mold cooling water control methods are roughly classified into a constant value flow rate control method, a method for controlling the surface temperature of a continuous cast piece to a constant value, and further the cooling water water described above. It can be divided into a method for controlling the temperature as a whole by taking into consideration the temperature difference ΔT, the molten steel temperature, and the like.

The constant value flow rate control method is a method of controlling the amount of cooling water supplied to the mold so that it is always a constant amount, and is the example shown in FIG. 3 described above. However, since the set flow rate of the cooling water is the same even in an unsteady state such as when the casting speed is reduced, the amount of excess cooling water has a large safety factor. Therefore, when the casting speed is lowered to stop casting and the top of the continuous cast piece is subject to overcooling when casting is stopped, it is necessary to continuously cast different steel grades with a large solidification shrinkage rate. The problem occurs due to the collapse of the shell.

The method of controlling the surface temperature of the continuous cast piece to be constant is a method of controlling the cooling rate mainly in the secondary cooling zone so that the surface temperature of the continuously cast piece produced literally becomes constant. It is not possible to prevent overcooling of the primary cooling in the mold and the resulting collapse of the shell.

Further, as a method of controlling the temperature as a whole by taking into consideration the cooling water temperature difference ΔT, the molten steel temperature, etc., it is disclosed, for example, in Japanese Patent Laid-Open Nos. 49-107928 and 52-46331. In addition, a method is known in which the relationship between the amount of cooling water passing through the mold and the amount of heat removal obtained from ΔT, and the relationship between the continuous casting speed and the like are set as constant conditions. However, these methods are mainly used when a change in ΔT is detected.
That is, since the amount of cooling water, the casting speed, and the like are controlled after the change in ΔT, it is not possible to deal with a sudden change in conditions such as the above-described reduction in casting speed for stopping the casting.

On the other hand, in Japanese Patent Laid-Open No. 187457/1985, in addition to the cooling water amount and ΔT, the casting temperature of the molten steel is further detected, and the molten steel heating degree (the molten steel temperature in the tundish obtained from the molten steel composition and its freezing point) is detected. And the difference between the freezing point obtained from the molten steel component) and the amount of cooling water based on the ΔT and the molten steel level in the mold. However, since the molten steel heating degree hardly changes at the end of casting, such as when the casting is stopped, this method cannot respond well to these unsteady times, and like the previous method, it does not respond to changes in ΔT, etc. Therefore, it is not possible to cope with a sudden change in conditions such as a reduction in casting speed for stopping casting.

That is, these conventional control methods for mold cooling water are intended for the operation of sound and stable continuous casting in steady-state continuous casting, and in the non-steady state, for example, as shown in FIG. It is not possible to cope with a sudden change in casting speed such as a decrease in casting speed for stopping casting as shown. Therefore, during non-steady state, especially when changing the steel type for continuous casting of different steel types or during casting speed change or casting stoppage during continuous casting of the same steel type after tundish exchange, etc., supercooling or insufficient cooling occurs, and the shell collapses. However, breakout and bleeding cannot be prevented, and a mold cooling water control method that solves these problems is desired.

An object of the present invention is to solve the above-mentioned problems of the prior art. When the casting speed changes during non-steady state, especially when the casting speed is reduced or the casting is stopped in continuous casting of different steel types, It does not cause bleeding or breakout due to insufficient cooling, and even if it has a high solidification shrinkage ratio, it can prevent the shell from collapsing due to overcooling, etc. Provided is a cooling water control method for a continuous casting mold, which is capable of stably and safely performing continuous casting of different steel types.

[0018]

In order to achieve the above object, the present invention provides a cooling water control method for a continuous casting mold in an unsteady state in continuous casting in which a steady state and an unsteady state are repeatedly operated. Then, when the difference between the temperature of the cooling water supplied to the continuous casting mold and the temperature of the cooling water discharged from the continuous casting mold is ΔT, the continuous casting is performed in accordance with the decrease in the continuous casting speed. The continuous casting so as to gradually decrease the amount of cooling water supplied to the casting mold and gradually increase the ΔT, and gradually increase the amount of cooling water supplied to the continuous casting mold and gradually decrease the ΔT according to an increase in the continuous casting speed. Provided is a cooling water control method for a continuous casting mold, which comprises controlling the supply of cooling water to the casting mold.

Further, it is preferable to control the supply of the cooling water according to a change in casting speed for stopping and starting continuous casting.

Hereinafter, a cooling water control method for the continuous casting mold of the present invention (hereinafter referred to as a cooling water control method)
Will be described in detail. FIG. 1 conceptually shows an upper portion of a continuous casting facility (hereinafter referred to as a continuous casting machine) for carrying out the cooling water control method of the present invention. In the continuous casting machine 10 shown in FIG. 1, molten steel is fed from a ladle (not shown) to a tundish 16
Is injected into the tundish 16 from the immersion nozzle 1
8 is injected into the mold 20.

The molten steel injected into the mold 20 starts solidification (forms a so-called shell) by primary cooling and becomes a continuous cast piece 12, which is drawn out to the secondary cooling zone 22. The secondary cooling zone 22 is composed of a large number of slab support rollers 24, 24, 24, ..., Spray nozzles arranged in the gaps between the slab support rollers 24, and the like, as in a normal continuous casting machine. The piece 12 is pulled out, and while being conveyed, secondary cooling is performed by water spray, mist spray, or the like. Secondary cooling zone 22
Are provided with pinch roller pairs 26a, 26b ... Which serve as a driving force for pulling and transporting the continuous cast slab 12 at arbitrary intervals, and the transport controller 28 that controls the driving of the pinch roller pairs 26a, 26b. The transport speed of the slab 12, that is, the casting speed (drawing speed) is controlled.

In the continuous casting machine 10 of the illustrated example, the cooling water for the mold 20 for primary cooling is supplied from the cooling water supply device 30 to the mold 20 via the supply line 32, and is discharged from the drain line 34 to the cooling machine. Be served. A thermometer 36 for measuring the temperature (inlet temperature) of the cooling water supplied to the mold 20 is provided in the supply line 32, while the thermometer 36 is provided for the drain line 3
4, thermometers 38 for measuring the temperature (outlet temperature) of the cooling water discharged from the mold 20 are arranged.

In such a continuous casting machine 10, the transfer control device 28 and the cooling water supply device 30 are connected to the control device 40, and according to the instruction of the control device 40, the casting speed of the continuous cast piece 12 and the mold 20. Adjust the cooling water supply to the. Further, the control device 40 includes thermometers 36 and 38.
Is connected, and the measurement results of the inlet temperature and the outlet temperature of the cooling water of the mold 20 are sent.

Since the continuous casting machine 10 shown in FIG. 1 is a facility that utilizes the cooling water control method of the present invention, it is possible to stop and restart casting when replacing the tundish 16 or continuously casting different steel types. To change the casting speed (including when the casting is stopped),
When the casting speed changes in various unsteady conditions such as when changing the ladle, that is, the cooling water amount is gradually decreased according to the decrease of the casting speed to gradually increase ΔT, and the cooling water amount is gradually increased according to the increase of the casting speed. The cooling water supply amount to the mold 20 is adjusted so as to reduce ΔT.

That is, in the continuous casting machine 10 of the illustrated example, for example, when the casting speed is lowered at the end of casting for the purpose of stopping the casting, the controller 40 instructs the transfer controller 28 to lower the casting speed. Cooling water supply device 30
The amount of cooling water supplied from is controlled (decreased) to increase ΔT.

FIG. 2 shows an example of the control of the cooling water supply amount of the present invention accompanied by the change in the casting speed at the time of stopping (ending) the casting of the previous steel type and starting the next casting in the successive casting of different steel types. .

In the example shown in FIG. 2, the casting speed is 0.8 m / min in the steady state, the mold cooling water supply amount is 2200 L (liter) / min, and ΔT is 4 at that time.
℃. The injection of molten steel from the ladle to the tundish 16 was completed, and at the end of casting, the T / D weight ratio (weight ratio of tundish to tundish weight during steady casting) was 58%. When the control device 40 receives the signal, the control device 40 instructs the transfer control device 28 to set the casting speed to 0.6 m / min to decrease the casting speed,
At the same time, the cooling water supply amount from the cooling water supply device 30 is set to 110
At 0 L / min, ΔT is raised to 7 ° C.

When the control device 40 receives a signal that the T / D weight ratio reaches 50% as the casting progresses, the control device 40 instructs the transfer control device 28 to set the casting speed to 0.4 m / min. To reduce the casting speed, and at the same time, the cooling water supply device 30
ΔT is 7 when the cooling water supply from
Hold at ° C.

As the casting further progresses, the control device 40 changes to T
When the signal that the / D weight ratio becomes 42% is received, the control device 40 instructs the transfer control device 28 to set the casting speed to 0.2 m / min to reduce the casting speed, and at the same time, the cooling water supply device 30. ΔT when the cooling water supply from the tank is 800 L / min
To 7.5 ° C. When the T / D weight ratio becomes 33%, the immersion nozzle 18 of the tundish 16 is closed and the pouring is completed, and the control device 40 causes the transfer control device 2 to operate.
An instruction to set the casting speed to 0 m / min (that is, conveyance stop) is issued to 8, and at the same time, the cooling water supply amount from the cooling water supply device 30 is set to 750 L / min and ΔT is maintained at 7.5 ° C. That is, the change in ΔT from the steady state at this time is 3.5 ° C.

When casting is stopped, "Tundish 16 movement of previous steel type" → "Partition material (connecting jig) insertion" →
"Shell collapse part seal implementation (whisker addition)" →
Various operations such as "arrangement of new tundish 16" → "start of injection of molten steel from new ladle into new tundish 16" → "open immersion nozzle 18 of new tundish 16 (start pouring)" are performed.

At the time when the T / D weight ratio reaches 33% after the start of casting, the control device 40 instructs the transfer control device 28 to set the casting speed to 0.2 m / min (that is, start the transfer). At the same time, the cooling water supply amount from the cooling water supply device 30 is set to 8
Then, the casting of the next steel grade is started with ΔT set to 00 L / min and ΔT kept at 7.5 ° C. After that, the control device 40 sequentially increases the casting speed according to the molten steel injection amount of the tundish 16, and accordingly adjusts the cooling water supply amount from the cooling water supply device 30 to reduce ΔT.

The conventional mold cooling water control method is intended for a sound and stable continuous casting operation in a steady state, and mainly detects a change in ΔT and accordingly supplies the cooling water or the cooling water. By adjusting the casting speed, it is intended to perform stable operation under constant conditions of primary cooling in the steady state of continuous casting. However, in these cooling water control methods, it is not possible to cope with a sudden change in the casting speed at various unsteady times such as a decrease in the casting speed for stopping the casting, and for example, in the case of changing the steel type of different steel types one after another. At this time, if the previous steel type has a high solidification shrinkage, the shell of the continuous cast piece top part collapses greatly when the casting is stopped, and the partition material cannot be inserted.
As described above, there are problems such as the inability to cast the next steel grade.

On the other hand, in the cooling water control method of the present invention, instead of the change of ΔT as in the conventional case, the change of the casting speed at the non-steady state, especially the rapid decrease of the speed for stopping the casting, etc. The amount of cooling water supplied to the mold 20 is controlled so that the cooling water amount is gradually decreased to gradually increase ΔT according to the decrease in the casting speed, and the cooling water amount is gradually increased to gradually decrease ΔT according to the increase in the casting speed. . According to the present invention as described above,
Even in a non-steady state involving a rapid change in casting speed such as a reduction in casting speed for stopping the casting shown in FIG.
Stable and safe continuous casting of different steel types and continuous casting after replacement of the tundish 16 as described above, by suitably preventing large collapse of the shell due to supercooling of (molten steel) and bleeding or breakout due to insufficient cooling. It can be carried out.

In the cooling water control method of the present invention, the maximum value of ΔT is preferably 12 ° C. or less, although it is somewhat different depending on the type of steel (solidification shrinkage ratio), the width of the slab, and the like. When ΔT exceeds 12 ° C, the possibility of bleeding or breakout increases, and safe and stable continuous casting may not be performed in some cases, although it depends on the type of steel and the like.

In the cooling water control method of the present invention, the cooling water amount is gradually decreased to increase ΔT in accordance with the decrease of the casting speed, and the cooling water amount is gradually increased to decrease ΔT in accordance with the increase of the casting speed. It is not clear why primary cooling can prevent bleeding and breakout due to insufficient cooling, and further prevent significant collapse of the shell. When the steel is supercooled, four rounds of the top portion shrink in the steel type having a high solidification shrinkage rate, and the shell falls inward to form a tapered shape. Therefore, shrinkage can be prevented by reducing the cooling amount and the amount of heat from the slab. In addition,
In the present invention, when the shrinkage ratio is high, 0.980 (actual width /
It is effective when the width is less than or equal to the command width, but the smaller the casting width is, the larger the temperature decrease amount of the slab becomes and the more the shrinkage amount is, so that the narrow width material is also effective.

If the cooling water control method of the present invention is performed when the casting speed is 0.7 m / min or less,
A particularly suitable effect is obtained.

The mold cooling water control method of the present invention as described above can be applied to various known continuous casting machines such as a vertical continuous casting machine, a vertical bending continuous casting machine, and a curved continuous casting machine. . In addition, the cooling water control method of the present invention is used only in the non-steady state,
In the steady state, the conventional cooling water control method disclosed in the above-mentioned JP-A-60-178457 may be used together.
Further, as the mold refrigerant, various refrigerants other than water can be used.

Although the cooling control method for the continuous casting mold of the present invention has been described in detail above, the present invention is not limited to the above examples, and various improvements and changes can be made without departing from the scope of the present invention. Of course you can go.

[0039]

EXAMPLES The present invention will be described in more detail with reference to specific examples of the present invention. <Invention example> Using a fully curved continuous casting machine with a machine length of 19.6 m,
C: 0.06, Si: 0.45, Mn: 0.60, Ni: 8.4, Cr: 18.4 (each wt%)
110 ton of continuous molten SUS304 steel having the composition The width of the mold (slab size) is 1240 mm,
A thickness of 200 mm (that is, similar to the example shown in FIG. 4 described above) was used.

After the injection of the molten steel from the ladle into the tundish is completed, the casting speed is lowered and the mold cooling water is controlled (that is, the cooling water control method of the present invention) in exactly the same manner as the example shown in FIG. ) Was performed and the casting was stopped. In addition,
The maximum value of ΔT at this time is 7.5 ° C, ΔT from the steady state
It is shown in FIG. 2 that the change in is 3.5 ° C. After stopping casting, "Move old tundish" → "Insert partition material" →
Perform each operation of "Implementation of shell collapse part" → "New tundish arrangement", inject SUS304 steel of the same composition from the ladle into the new tundish, restart the injection of molten steel into the mold from the new tundish, Successive casting of SUS304 steel was performed. As a result, bleed and breakout,
It was possible to perform continuous casting after the tundish replacement without any problem without causing the shell to collapse significantly.

<Comparative Example> For comparison, continuous casting was performed in exactly the same manner as in the Example of the present invention except that the cooling water control was changed. The cooling water control conditions are as follows. Method A: The amount of cooling water was always constant (that is, FIG.
As a result, in the method A, as shown in FIG. 4, the shell fell significantly, and the slab support roll could be seen from above the mold.
From the above results, the effect of the present invention is clear.

[0042]

As described above in detail, according to the cooling water control method of the continuous casting mold of the present invention, the continuous cast piece ( A large collapse of the shell due to supercooling of molten steel,
Bleeds, breakouts, etc. due to insufficient cooling can be suitably prevented, and continuous casting of different steel types as described above or continuous casting after the tundish replacement can be stably and safely performed, which is extremely effective in contributing to productivity.

[Brief description of drawings]

FIG. 1 is a view conceptually showing an example of a continuous casting facility for carrying out the cooling water control method for a continuous casting mold of the present invention.

FIG. 2 is a graph showing an example of a cooling water control method for a continuous casting mold according to the present invention.

FIG. 3 is a graph showing an example of a conventional cooling water control method for a continuous casting mold.

FIG. 4 is a diagram conceptually showing an example of the collapse of a shell by a conventional cooling water control method for a continuous casting mold.

[Explanation of symbols]

 10 Continuous casting equipment (continuous casting machine) 12 Continuous cast pieces (continuous cast pieces) 16 Tundish 18 Immersion nozzle 20 Continuous casting mold (mold) 22 Secondary cooling zone 24 Cast piece support rollers 26a, 26b Pinch roller 28 Transfer control Device 30 Cooling water supply device 32 Supply line 34 Drain line 36, 38 Thermometer 40 Control device

Claims (2)

[Claims] 1. A method of controlling cooling water for a continuous casting mold in a non-steady state in continuous casting in which a steady state and an unsteady state are repeatedly operated, the temperature of cooling water being supplied to the continuous casting mold. When the difference from the temperature of the cooling water discharged from the continuous casting mold is ΔT, the amount of cooling water supplied to the continuous casting mold is gradually decreased according to the decrease in the continuous casting speed to gradually increase ΔT. ,
Continuous casting characterized in that the cooling water supply to the continuous casting mold is controlled so that the amount of cooling water supplied to the continuous casting mold is gradually increased and the ΔT is gradually decreased according to an increase in the continuous casting speed. Water control method for casting mold. 2. The cooling water control method for a continuous casting mold according to claim 1, wherein the control of the cooling water supply is performed according to a casting speed change for stopping and starting the continuous casting.