JPH06304711A - Twin roll type continuous casting method - Google Patents

Abstract

PURPOSE:To provide a twin roll type continuous casting method for obtaining a metal strip having fine crystal grain and excellent workability and surface characteristic by rapidly solidifying and cooling molten metal. CONSTITUTION:A rolling reduction cooling roll 4 is arranged below the cooling rolls 1a, 1b and at first, the cast strip 3 is separated from the cooling rolls and introduced to the contacting point 5 between the cooling roll and the rolling reduction cooling roll in the non-contacting condition. Successively, the cast strip is rolled with the rolling reduction cooling roll at <=20% rolling reduction ratio and thereafter, the cast strip is run while bringing into contact with the peripheral surface of the rolling reduction cooling roll and rapidly cooled in this contacting section at >=700 deg.C/sec cooling velocity. By this method, the crystal grain is made to be fine with small rolling reduction capacity, and the cast strip having beautiful surface can be obtd. and also, even after rolling in the following process, the metal strip having excellent surface characteristic is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method of casting a molten metal such as a ferrous metal, a non-ferrous metal or an alloy thereof, followed by rapid solidification and cooling,
The present invention relates to a twin roll continuous casting method for forming a metal thin plate having fine crystal grains and excellent in workability and surface properties.

[0002]

2. Description of the Related Art A twin roll type continuous casting method for producing a thin metal sheet by injecting molten metal between a pair of cooling rolls rotating inward and rapidly solidifying the molten metal is known as a Bessemer method. According to the method, it is possible to simplify the process and equipment, because the conventional hot rolling process in multiple stages is not required and the rolling to the final shape is also light.

FIG. 4 shows an example of an apparatus for carrying out this twin roll type continuous casting method. FIG. 4 (a) is a schematic side view, and FIG.
The figure is a bird's eye view. In this casting device, a pair of cooling rolls 11a and 11b that rotate in mutually opposite directions are arranged at appropriate intervals, and both side ends in the roll axial direction are side dams 12a and 12b.
Partitioned by b to form the hot water pool 13.

When molten metal is poured into the pool 13 from above and rotated inwardly, the molten metal injected comes into contact with the cooling rolls 11a and 11b and is removed from the heat. As a result, the respective cooling rolls are removed. Solidified shell 14 on the surface
Is formed. The solidified shell 14 is joined as the roll rotates while it is growing, and is further pressed by the roll gap 15 to form a thin plate cast piece 16 having a predetermined thickness, which is fed below the roll to manufacture a thin metal plate.

[0005]

In the case of this casting method,
Since the molten metal is rapidly cooled and solidified, the solidified shell in the pool holds fine crystal grains. However, the thin cast slab sent out from the cooling roll gap is still in a high temperature state, and there is a large temperature difference between the surface layer part of the slab and the center part of the plate thickness that are in contact with the cooling roll, and it contains an unsolidified part inside. In some cases.

The heat retained by the high temperature layer inside the thin cast piece is transferred by heat conduction to the surface layer portion after the thin cast piece exits from the cooling roll gap, and the temperature of the surface layer rises, that is, reheats. It has been confirmed that the thin cast piece has coarse crystal grains over the entire plate thickness.

This coarsening of crystal grains is caused by surface defects when the final product is subjected to the conventional manufacturing process of pickling-cold rolling-annealing in the present process omitting the hot rolling process of performing a certain reduction. It is known to cause the occurrence of. For example, when a thin-walled slab of stainless steel produced by twin roll type continuous casting is directly processed into a product in the conventional production process without hot rolling, rough skin and uneven luster called roping occur, Remarkably reduce the commercial value.

Two methods have been proposed for such a problem. The first is to rapidly cool the thin-walled slab sent out from the cooling roll gap at 700 ° C./sec or more to maintain the crystal grains at a grain size of 50 μm or less, and the second
Is thought to be performed by subjecting a thin cast piece after casting to hot rolling at a reduction rate of 50% or more to refine the crystal grains, and the effect on the refinement of the crystal grains by hot rolling is considered to be The higher the temperature of the thin cast piece, the more remarkable.

To solve such a problem, for example, in Japanese Unexamined Patent Publication No. 2-247049, a thin cast piece immediately after the completion of solidification is made to travel by a pressing roll in a state of being in contact with the cooling roll and passing through the cooling roll. 1250 to 11 at a cooling rate of 200 ° C / second or more
A technique of rapidly cooling to a temperature range of 00 ° C is disclosed.

In this technique, the cooling rate of the thin-walled slab is 200 to 500 ° C./sec. 10-40%
Is hot-rolled. The method proposed by this technology is
Since the temperature of the thin-walled slab is lowered rapidly by cooling, the rolling resistance of the slab itself becomes large against the reduction necessary for the refinement of the initial γ crystal grains, so a rolling machine with a larger capacity is required. There is a problem of becoming.

Further, Japanese Unexamined Patent Publication No. 1-87045 discloses a reduction device in which one of the pair of cooling rolls is used as a work roll and a work roll supported by a backup roll is arranged on the opposite side. This reduction device is intended to prevent vibration, blurring, meandering, etc. during the transportation process of a thin cast product, and at the same time, to reduce the size of the structure by reduction.
It is not intended to miniaturize the structure by positively quenching the slab with the work roll.

The present invention has been made in view of the above problems,
A twin-roll continuous casting method for rapidly solidifying and cooling a molten metal by adding a cooling roll to form a thin metal plate having fine crystal grains and excellent workability and surface properties.

[0013]

DISCLOSURE OF THE INVENTION The present invention is a twin roll continuous casting method for producing a thin cast piece by rapidly solidifying molten metal injected between a pair of cooling rolls. Providing a pressure-down cooling roll that incorporates cooling means and presses the roll, first guide the cast thin-walled slab from the cooling roll to the contact point between one cooling roll and the pressure-down cooling roll in a non-contact state, Then, the thin-walled slab is rolled at a reduction rate of 20% or less by a reduction chill roll, and then the thin-walled slab is run while being in contact with the peripheral surface of the reduction chill roll, and the thin-walled slab is rapidly cooled in this contact section. This is a characteristic twin-roll type continuous casting method.

In the twin roll type continuous casting method, until the casting is started and the casting speed reaches a steady state,
The reduction cooling roll is adjusted to be slower than the peripheral speed of the cooling roll.

In the twin roll type continuous casting method, at least one of the temperature difference between the inlet side and the outlet side of the internal cooling water of the pair of cooling rolls, the surface temperature of the cooling rolls and the temperature of the thin cast piece is constantly detected. The contact state between the chill roll and the thin slab is monitored, and if contact between the chill roll and the thin slab is detected, the peripheral speed of the reduction roll is adjusted to be slower than the peripheral speed of the chill roll, and no contact is made. It is to restore the state.

Further, in the above twin roll type continuous casting method, at least one of the temperature difference between the inlet side and the outlet side of the internal cooling water of the reduction cooling roll and the surface temperature of the reduction cooling roll is always detected to detect the reduction cooling roll. And the contact state of the thin-walled slab is monitored, and when the state where the thin-walled slab detaches too much from one of the cooling rolls and hangs down is detected, the peripheral speed of the reduction cooling roll is adjusted faster than the peripheral speed of the cooling roll. It is intended to be restored.

Here, in order to restore the contact state and the hanging state of the thin-walled slab to the optimum non-contact state, the peripheral speeds of one of the cooling rolls and the reduction cooling roll are adjusted. Is the binding pressure of the thin-walled slab is larger than that of one of the cooling rolls by the surface pressure of the area wound around the reduction cooling roll, and if the peripheral speed of the reduction cooling roll is changed, one of the cooling rolls The gap between the one cooling roll and the thin cast piece can be restored by slipping between the thin cast piece and the thin cast piece.

[0018]

According to the experiments conducted by the present inventor, when a molten metal is injected between a pair of cooling rolls and rapidly cooled and solidified to be cast into a thin plate, the thin-walled slab immediately after casting is still in a molten state inside. Alternatively, it maintains a high temperature close to the molten state.

While the thin cast slab is transferred to the reduction cooling roll, it is separated from the chill roll by a certain distance to bring it into a non-contact state, and the temperature of the entire thin slab is near the solidification temperature by the recuperation action during this period, for example, SUS304 stainless steel. Then 130
The rolling surface is uniformly reheated to 0 to 1400 ° C in the sheet thickness direction to reduce the rolling resistance. After that, the rolling cooling roll rolls a light rolling reduction at a rolling reduction of 20% or less, and further includes a cooling means built-in peripheral surface. The thin-walled slab is rapidly cooled at a cooling rate of 700 ° C./sec or more while traveling for a certain period while contacting with.

Here, the reduction ratio of the thin-walled slab by the reduction chill roll is set to 20% or less because the high-pressure region near the solidification temperature where the highest pressure is required to refine the crystal grains of the thin-walled slab. With a reduction rate of 20%, the grain size was sufficiently refined,
For example, SUS304 stainless steel is based on the experimental result that 50 μm or less could be secured.

As a result of observing the thin cast piece produced by this method, it was confirmed that the crystal grains were made finer, and that this method was effective for making the crystals finer. That is, in the present invention, the thin cast piece immediately after casting is once released from the cooling roll to reheat the cast piece, the rolling resistance is reduced, light reduction is applied, and then the material is rapidly cooled, whereby the crystal grains are refined. A thin slab was obtained, and a metal plate with excellent surface quality without roping or uneven gloss was obtained even after rolling in the subsequent step.

Further, in the present invention, while the cast thin cast piece is guided to the contact point between the cooling roll and the reduction cooling roll, the cast piece is separated from the cooling roll by a certain distance to be in a non-contact state. When this distance fluctuates during casting and comes too close to the chill roll, and when it comes into contact with the chill roll, the slab is excessively cooled by the chill roll. For example, in the case of SUS304 stainless steel, the slab is also reheated. After being cooled to 1300 ° C. or less, the rolling resistance of the rolling roll is increased.

Therefore, in the present invention, at least one of the temperature difference between the inlet side and the outlet side of the internal cooling water of the cooling roll, the surface temperature of the cooling roll or the temperature of the thin cast piece is constantly detected,
Increase in temperature difference of cooling water, increase in surface temperature of cooling roll,
Alternatively, when a decrease in the temperature of the thin slab is detected, it means that the thin slab is too close to one of the cooling rolls, and this is corrected by adjusting the peripheral speed of the reduction cooling roll to be slower than that of the cooling roll. Here, if the reduction force of the reduction cooling roll is reduced, slip flaws hardly occur in the thin cast piece.

Further, if the thin slab comes away from one of the cooling rolls, that is, if the slab hangs down, the thin slab comes into contact with the reduction cooling roll before the contact point, and The temperature decreases and the rolling resistance increases.

Therefore, at least one of the temperature difference between the inlet side and the outlet side of the internal cooling water of the reduction cooling roll and the surface temperature of the reduction cooling roll is constantly detected to increase the temperature difference of the cooling water, If a rise in the surface temperature is detected, the thin cast piece is too detached from one of the cooling rolls and hangs down, and is restored by adjusting the peripheral speed of the reduction cooling roll faster than the peripheral speed of the cooling roll. To do. Here, if the reduction force of the reduction cooling roll is reduced, slip flaws hardly occur in the thin cast piece.

[0026]

FIG. 1 is a schematic side view showing an example of a twin roll type continuous casting apparatus suitable for carrying out the casting method of the present invention.
A pair of cooling rolls 1a and 1b rotating in opposite directions are arranged at appropriate intervals, molten metal is injected into the formed pool 2 and is cooled and solidified by the cooling rolls 1a and 1b,
The thin cast piece 3 is cast.

Below one of the pair of cooling rolls 1a and 1b, below the one cooling roll 1a, there is provided a reduction cooling roll 4 which has a built-in cooling means and presses the cooling roll 1a. The thin cast piece 3 cast in 1b is separated from the cooling roll 1a by a predetermined distance t, and is guided between the contact points of the cooling roll 1a and the reduction cooling roll 4 in a non-contact state.

Next, when this thin cast piece 3 passes through the contact 5,
Rolling is performed by applying a reduction of 20% or less with a reduction cooling roll 4 and continuously passing the contact point 5 and rolling the thin cast slab 3 while contacting the reduction cooling roll peripheral surface with a constant section L on the peripheral surface. The thin cast slab 3 is made to run and rapidly cooled in this contact section L at a cooling rate of 700 ° C./sec or more to obtain a thin metal plate 6.

In this continuous casting apparatus, the temperature difference between the inlet side and the outlet side of the cooling water in the cooling roll, the cooling roll surface thermometer 7 for detecting the surface temperature of the cooling roll, or the surface temperature of the thin cast piece is measured. A sensor that constantly detects at least one of the thin-wall cast slab surface thermometers 9 is installed.

Further, a sensor for constantly detecting at least one of the reduced cooling roll surface thermometers 8 for detecting the temperature difference between the inlet side and the outlet side of the internal cooling water of the reduced cooling roll and the surface temperature of the reduced cooling roll is provided. Install. Or thin cast slab 3
The slack detector 10 may be installed at a position outside the.

In this way, the non-contact state between the cooling roll 1a and the thin cast slab 3 or the degree of sagging of the slab is detected, and the thin cast slab 3 is controlled so as to be always separated from the cooling roll 1a by a constant distance t. , The temperature of the thin cast piece 5 guided to the contact point 5 is properly maintained.

FIG. 2 shows the temperature difference between the inlet side and the outlet side of the internal cooling water of the pair of cooling rolls when one cooling roll and the thin casting are in contact, and FIG. The experimental results of the temperature difference between the inlet side and the outlet side of the internal cooling water of the pressure-reducing chill roll when the chill roll excessively separated from the chill roll and drooped were shown.

As described above, the thin-walled slab just after casting is once released from the cooling roll to reheat the slab, the rolling resistance is lowered to apply a light reduction, and then the slab is rapidly cooled to make the crystal grains fine. As a result, the workability of the slab is improved and a beautiful surface can be obtained.

[0034]

As described above, according to the twin roll type continuous casting method of the present invention, the cast thin slab is once released from the cooling roll to reheat the slab to reduce the rolling resistance and reduce the rolling reduction to 20. %, And then rapidly cooled at a cooling rate of 700 ° C / sec or more, the crystal grains of the thin cast slab are refined by the reduction chill roll with a small reduction capacity, and the workability is also improved. It is possible to obtain a slab with a smooth surface, and also to obtain a metal thin plate having excellent surface properties without roping, rough skin, uneven gloss, and wrinkles even after rolling in a subsequent process.

[Brief description of drawings]

FIG. 1 is a schematic side view showing a twin roll type continuous casting apparatus suitable for carrying out the casting method of the present invention.

FIG. 2 is a diagram showing an experimental result of measuring a temperature difference between an inlet side and an outlet side of cooling water inside a cooling roll when a cooling roll and a thin cast piece are in contact with each other.

FIG. 3 is a diagram showing an experimental result of measuring a temperature difference between an inlet side and an outlet side of cooling water inside a reduction cooling roll when a thin cast piece is excessively separated from the cooling roll.

FIG. 4 shows an example of a conventional twin roll type continuous casting device,
(A) is a schematic side view, and (b) is a bird's-eye view thereof.

[Explanation of symbols]

 1a, 1b Cooling roll 2,13 Hot water pool 3,16 Thin cast slab 4 Rolling down cooling roll 5 Roll contact point 6 Metal thin plate 7 Cooling roll surface thermometer 8 Rolling down cooling roll surface thermometer 9 Thin casting surface thermometer 10 Casting Piece loosening detector 11a, 11b Cooling rolls 12a, 12b Side weir 14 Solidification shell 15 Roll gap

Claims (4)

[Claims] 1. A twin roll type continuous casting method for producing a thin cast piece by rapidly solidifying molten metal injected between a pair of cooling rolls, wherein a cooling means is built in below one cooling roll and the roll is formed. Provide a reduction cooling roll to press
First, the cast thin-walled slab is released from the cooling roll and guided to the contact point between one cooling roll and the reduction cooling roll in a non-contact state, and then the thin-walled slab is rolled by the reduction cooling roll at a reduction rate of 20% or less. Then, the thin-walled slab is then run while contacting the peripheral surface of the reduction cooling roll, and the thin-walled slab is cooled in this contact section. 2. When the twin roll type continuous casting is started, the reduction cooling roll is adjusted to be slower than the peripheral speed of the cooling roll until the casting is started and the casting speed reaches a steady state. Item 2. The twin roll continuous casting method according to Item 1. 3. The cooling roll and the thin wall casting are constantly detected by at least one of the temperature difference between the inlet side and the outlet side of the internal cooling water of the pair of cooling rolls, the surface temperature of the cooling roll and the temperature of the thin cast piece. The contact state of the piece is monitored, and when the contact between the cooling roll and the thin cast piece is detected, the peripheral speed of the reduction cooling roll is adjusted to be slower than the peripheral speed of the cooling roll to restore the non-contact state. The twin roll type continuous casting method according to claim 1. 4. The contact state between the reduction chill roll and the thin-walled slab is constantly detected by detecting at least one of the temperature difference between the inlet side and the outlet side of the internal cooling water of the reduction chill roll and the surface temperature of the reduction chill roll. When it is detected that the thin cast piece has dropped too much from one of the cooling rolls and is hanging down, it is restored by adjusting the peripheral speed of the reduction cooling roll faster than the peripheral speed of the cooling roll. The twin roll type continuous casting method according to claim 1.