JPH0751807A - Twin roll type continuous casting method - Google Patents

Abstract

PURPOSE:To provide a twin roll type continuous casting method for obtaining a thin metal sheet having fine crystal grain and excellent workability and surface characteristic by holding a molten metal pool in the mixed gas atmosphere and rapidly cooling the molten metal. CONSTITUTION:In this method, a closed box type frame 3 surrounding the molten metal pool part 2 and a rolling reduction cooling roll 6 are arranged below one pair of cooling rolls 1a, 1b. At first, the inner part of the box type frame is held to gaseous helium atmosphere or mixed gas atmosphere of two or more kinds among the helium, argon and nitrogen having >=0.5kg/cm<2> and <=100mW/mk thermal conductivity. The molten metal is poured into the box type frame to form the molten metal pool part 2 kept to a fixed molten metal static pressure. Successively, the rolling reduction is applied to solidified shells 7a, 7b to make the thin cast slab 9, and this cast slab is introduced to a contact point 10 while bringing the cast slab into contact with the peripheral surfaces of the cooling rolls. After passing through the contact point, the cast slab is run while contacting with the peripheral surface of the rolling reduction cooling roll and rapidly cooled at 700 deg.C/sec cooling rate. By this method, the fining of the crystal grain is achieved without passing through a hot rolling process and the cast slab having excellent workability is obtd. and further, the thin metal sheet having excellent surface characteristic can be 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. 2 shows an example of an apparatus for carrying out this twin roll type continuous casting method. In this apparatus, a pair of cooling rolls 21a and 21b rotating in opposite directions are arranged at appropriate intervals, and a roll shaft is provided. Both ends in the direction are side weirs 22a, 22b
The hot water pool 23 is formed by partitioning.

When the molten metal is poured into the pool 23 from above and rotated inwardly, the molten metal is brought into contact with the cooling rolls 21a and 21b, and the heat is removed, resulting in the respective cooling rolls. Solidified shells 24a, 24b are formed on the surfaces of 21a, 21b. The solidified shells 24a, 24b grow and cool the cooling rolls 21a, 21b.
They are joined together with the rotation of b, and are further rolled down by the roll gap 25 to form a thin plate cast piece 26 having a predetermined thickness, which is delivered below the cooling rolls 21a and 21b to manufacture a thin metal plate.

In this system, since the molten metal is rapidly cooled and solidified, the solidified shells 24a and 24b of the pool portion 23 form fine crystal grains. However, the thin cast slab 26 sent out from the roll gap 25 is still in a high temperature state, and the temperature difference between the slab surface layer portion contacting the cooling rolls 21a and 21b and the plate thickness central portion is large, and the thin cast slab 26 is not solidified inside. May include parts.

The amount of heat retained by the high temperature layer inside the thin cast piece 26 is transferred by heat conduction to the surface layer portion after the thin cast piece 26 exits from the roll gap 25, and the temperature of the surface layer rises, that is, recuperation. Therefore, it has been confirmed that the thin cast slab 26 has a phenomenon in which crystal grains are coarsened 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 cast piece of stainless steel manufactured by twin-roll type continuous casting is directly processed into a product by the conventional manufacturing process without hot rolling, rough skin and uneven luster called roping occur. And significantly reduce the commercial value.

In order to solve such a problem, first, the thin cast piece fed from the roll gap is rapidly cooled at 700 ° C./sec or more to maintain the crystal grains at a grain size of 50 μm or less. It is considered that the thin-walled slab is subjected to hot rolling at a reduction rate of 50% or more to refine the crystal grains.

For example, in JP-A-58-97468 and JP-A-59-127954, tension is applied to a thin cast piece by a pinch roll to bring one cooling roll into close contact with the thin cast piece for rapid cooling. However, no specific reference is made to the occurrence of rough skin and uneven gloss called roping due to the coarsening of the crystal grains of the thin cast slab, and a method of suppressing the unevenness.

Further, in Japanese Unexamined Patent Publication No. 2-247049, in a method in which a pressing roll causes one of the cooling rolls to contact the thin-walled slab sent out from the cooling roll gap for rapid cooling, the cooling rate of the thin-walled slab is limited. 20
Since it is 0 to 500 ° C./sec, the grain size of the γ grain size is 50 μm by using the hot rolling process with a reduction rate of 40% or less.
It is said that the product has an excellent surface condition and material without causing defects such as roping and uneven gloss when rolled in a subsequent process.

[0012]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In JP97468 and JP-A-59-127954, a pinch roll is used to apply tension to a thin cast piece to bring one cooling roll into contact with the thin cast piece for rapid cooling. However, one cooling roll is used. No mention is made of the adjustment of the gap amount and the thermal resistance between the thin cast piece and the thin cast piece, and therefore, a cooling rate of 700 ° C / sec or more sufficient to achieve the crystal grain size of the thin cast piece of 50 μm or less is achieved. Can not.

The method described in JP-A-2-247049 is a method for refining crystal grains by subjecting a thin-walled slab in a high temperature state immediately after casting to hot rolling to reduce the size of crystal grains. Since the thin cast piece cannot be rapidly cooled at a cooling rate of 700 ° C./sec or more due to the heat removal between the cooling roll and the thin cast piece by the hot rolling equipment, an expensive hot rolling machine is required. It requires the installation of rolling and maintenance of rolling rolls, and does not utilize the original purpose of the twin-roll continuous casting method of omitting the hot rolling process.

In the experiment conducted by the present inventor, as described in Japanese Patent Application Laid-Open No. 2-247049, a thin-walled slab was removed by heat removal between one cooling roll and a thin-walled slab by a pinch roll or a pressing roll. Cooling rate is 700
C / sec could not be achieved.

The cause of this is that, especially when the outer peripheral surface of the cooling roll is provided with a concave dimple process aiming at the effect of slowly cooling the molten metal, the dimple is transferred to the thin cast piece to form an uneven shape. That is, between the one cooling roll and the thin cast piece is a great heat resistance of the air gap formed by the concave dimples on the outer peripheral surface of the roll itself and the unevenness of the thin cast piece, and also in the roll gap The outer peripheral surface temperature of the cooling roll was around 400 ° C., and it was revealed from the experimental results that the heat removal ability for the thin cast piece was low.

Further, as a countermeasure against the occurrence of surface defects such as roping and uneven gloss after cold rolling, it is effective to further rapidly cool the solidified shell in the pair of cooling rolls to make the crystal grains finer. Was obtained from the experimental results.

The present invention has been invented on the basis of the above knowledge to reduce the thermal resistance between the cooling roll and the solidification shell and the thin cast slab, that is, to reduce the gap amount between the cooling roll and the solidification shell. In order to increase the molten steel static pressure by increasing the molten metal surface, the gas medium existing in the gap between the cooling roll and the solidified shell and the thin-walled slab is set to 100 m.
The solidified shell and the thin cast piece are rapidly cooled by a method of substituting with a gas having a thermal conductivity of W / m · K or more to maintain the crystal grains at 50 μm or less.

The present invention does not undergo a hot rolling process, which is one of the advantages of the twin roll type continuous casting method, and produces surface defects when the final product is produced by the conventional pickling-cold rolling-annealing process. It is an object of the present invention to provide a method and an apparatus for producing a thin-walled cast product having a product free from defects and having good mechanical properties such as elongation.

[0019]

DISCLOSURE OF THE INVENTION The present invention provides a twin roll type continuous casting method for injecting molten metal into a molten metal pool formed between a pair of cooling rolls and rapidly solidifying the molten metal to produce a thin cast piece. In the upper part of the cooling roll, a box form which encloses and seals the hot water pool over the entire width thereof, and a pressing cooling roll for pressing the thin cast piece to one cooling roll below the pair of cooling rolls are arranged, First, 100 mW / mK in the box form
Helium gas having the above thermal conductivity, or a mixed gas of two or more kinds of helium, argon, and nitrogen can be used in a range of 0.
The molten metal was poured into the box form to maintain a constant static pressure while maintaining an atmosphere of 5 kg / cm ² or more to form a pool of water, and then solidification formed on the cooling roll surface of the pool of water. The shell is rolled by passing it through a roll gap to cast a thin-walled slab, and the thin-walled slab cast is guided to a contact point between the roll and the pressure-reducing cooling roll while contacting one of the cooling roll peripheral surfaces, and the contact point After passing through, the twin-wall continuous casting method is characterized in that the thin-walled slab is caused to come into contact with the peripheral surface of the reduction cooling roll to run, and the thin-walled slab is cooled in the cooling process of each of the cooling roll and the reduction cooling roll.

[0020]

Compared with the conventional twin roll type continuous casting, the present invention is
First, a box form surrounding the hot water pool is installed on the upper part of the cooling roll, and the inside of the box form is helium gas having a thermal conductivity of 100 mW / m · K or more, or two kinds of helium, argon and nitrogen. While maintaining an atmosphere of 0.5 Kg / cm ² or more with the above mixed gas, injecting molten metal into the box form, pressurizing the molten metal pool with this helium gas or mixed gas atmosphere pressure to maintain a constant static pressure. I try to maintain the pressure. Therefore, the amount of the gap between the chill roll and the solidifying shell, which is generated during solidification, is decreased by the increase in the static pressure, and the contact is intimate.

Here, the atmospheric pressure in the pool is 0.5 kg.
If it is less than / cm ² , the gap amount between the cooling rolls 1a, 1b and the solidification shells 7a, 7b will not be reduced, and the crystal grains of the solidification shells 7a, 7b in the pool will not be sufficiently miniaturized. Not good for

Further, since this atmospheric gas has a high thermal conductivity, the amount of heat removed between the cooling roll and the formed solidified shell is increased to rapidly cool the solidified shell.

Also, in the process of cooling and running the cast thin-walled slab while contacting the peripheral surface of one of the cooling rolls and further to the cooling roll for reduction, as the casting progresses, the atmospheric gas having this high thermal conductivity is cooled by the ambient gas. ， Because it is possible to hold the reduction slab on the peripheral surface, the cooling efficiency of the thin slab is improved even in this process, and the thin slab is 700 ℃
It becomes possible to perform rapid cooling at a cooling rate of / second.

Table 1 shows the thermal conductivity of helium gas, argon gas, nitrogen and air used as the pressurized atmosphere gas in the present invention at around 1000K.

In the present invention, the thermal conductivity of the atmosphere gas is set to 100 mW / mK or more because the thermal conductivity of the argon gas is 43.5 mW / mK.
Since it was found from the experimental result that the thin cast piece has an effect of being rapidly cooled at 700 ° C./sec.

[0026]

[Table 1]

As described above, according to the present invention, when casting a thin cast slab by the twin roll type continuous casting apparatus, a box form surrounding the molten metal pool is installed, and the molten metal is cooled by the helium gas or mixed gas atmosphere pressure. The pressure is increased to reduce the amount of the gap between the cooling roll and the solidified shell, and the roll including the molten metal pool is also kept in the helium gas or mixed gas atmosphere having high thermal conductivity.

Therefore, the cooling efficiency of the solidified shell and the thin-walled slab is improved, and the slab is rapidly cooled at a cooling rate of 700 ° C./sec. Therefore, the crystal grains of the thin-walled slab are refined to 50 μm or less, and the workability is improved. It is also possible to obtain a metal thin plate having excellent surface properties without roping, rough skin, uneven gloss, and wrinkles.

[0029]

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.

In the present casting apparatus, a pair of cooling rolls 1a and 1b that rotate in opposite directions are arranged at appropriate intervals, and a cooling pool 1a and 1b is hermetically sealed to surround the pool 2 over the entire width of the rolls. The box form 3 is placed. Reference numeral 4 is an injection nozzle from the tundish, and 5 is a nozzle for supplying and pressurizing helium gas into the closed box mold 3. Further, below the one of the pair of cooling rolls 1a, there is arranged a reduction cooling roll 6 which incorporates cooling means and presses the cooling roll 1a.

First, 100 m from the nozzle 5 into the box frame 3.
Helium gas having a thermal conductivity of W / mK or more, or a mixed gas of two or more kinds of helium, argon, and nitrogen is supplied and pressurized, and the inside of the frame is helium gas of 1.5 Kg / cm ² or more or a mixture. The molten metal is injected into the closed box mold 3 from the injection nozzle 4 while maintaining the gas atmosphere to form the pool 2 for maintaining a constant static pressure. The poured molten metal is cooled by the cooling rolls 1a, 1b in the pool 2 of water.
The surface is cooled to form solidified shells 7a, 7b.

The solidification shells 7a and 7b contract during solidification and are cooled by the normal cooling rolls 1a and 1b.
Although a gap is formed between a and 7b, it is compressed by the atmospheric pressure of helium gas or a mixed gas to reduce the gap amount, and the contact becomes dense. Then, the solidified shells 7a, 7b
Is thinned by the roll gap 8 as the cooling rolls 1a and 1b rotate, and a thin cast piece 9 is cast.

Further, the cast thin-walled slab 9 is guided to the contact point 10 between the roll 1a and the reduction cooling roll 6 while contacting the peripheral surface of the cooling roll 1a, and after passing through the contact point 10, the thin-walled slab 9 continues. Is brought into contact with the peripheral surface of the cooling roll 6 for rolling.

In the cooling process by the cooling rolls 1a and the reduction cooling rolls 5, since the helium gas or the mixed gas continues to be present between the rolls 1a and 5, the cooling efficiency of the thin cast slab 9 is also improved in this process. Then, the thin slab is rapidly cooled at a cooling rate of 700 ° C./sec to manufacture the metal thin plate 11.

The metal thin plate 11 manufactured in this way
Is a thin-walled slab with high workability in an atmosphere gas having a high thermal conductivity, and because the contact with each cooling roll is also kept close, cooling efficiency is improved, and the crystal of the slab is refined. Can be obtained. Further, since the atmospheric gas is inactive, it has an effect of preventing the molten metal and the thin cast piece from being oxidized.

[0036]

As described above, in the twin roll type continuous casting method of the present invention, the helium gas having the thermal conductivity of 100 mW / mK or more is provided by installing the closed box form surrounding the pool. Alternatively, it is easy to increase the static pressure of the molten metal by the atmospheric pressure of a mixed gas of two or more kinds of helium, argon, and nitrogen, and to keep the entire roll including the pool part in a helium gas or mixed gas atmosphere having high thermal conductivity. The cooling efficiency of the thin slab is improved by various means,
It is possible to quench rapidly at a cooling rate of / sec, and without cooling through the conventional hot rolling process, this cooling achieves the refinement of crystal grains while preventing the surface temperature of the slab from rising due to reheating of the slab. In addition, a slab with excellent workability can be obtained, and even after rolling in the post process, roping, rough skin, uneven gloss,
It is possible to obtain a thin metal plate having excellent surface properties without wrinkles.

[Brief description of drawings]

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.

FIG. 2 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 Hot water reservoir 3 Closed box form 4 Injection nozzle 5 Gas injection nozzle 6 Cooling roll 7a, 7b Solidified shell 8 Roll gap 9 Thin cast piece 10 Roll contact point 11 Thin metal plate 21a, 21b Cooling Rolls 22a, 22b Side weir 23 Hot water pool 24a, 24b Solidified shell 25 Roll gap 26 Thin cast piece

Claims (1)

[Claims] 1. A twin-roll continuous casting method for producing a thin cast piece by injecting molten metal into a molten metal pool formed between a pair of cooling rolls, and rapidly solidifying the molten metal to produce a thin cast piece. A box formwork that encloses and seals the hot water pool over the entire width thereof, and a reduction cooling roll that presses a thin cast piece against one cooling roll below a pair of cooling rolls are arranged. First, the inside of the box formwork is 100 mW / Helium gas having a thermal conductivity of m · K or more, or a mixed gas of two or more of helium, argon, and nitrogen is maintained in an atmosphere of 0.5 Kg / cm ² or more, and molten metal is contained in the box form. To form a molten metal pool portion maintained at a constant static pressure, then cast a thin cast piece by rolling down the solidified shell formed on the cooling roll surface of the molten metal pool portion through the roll gap,
Guide the cast thin-walled slab to one of the cooling roll peripheral surfaces while inducing it to the contact point between the roll and the reduction cooling roll, and after passing through the contact point, the thin-walled slab is allowed to travel in contact with the reduction cooling roll peripheral surface, A twin-roll continuous casting method, characterized in that a thin cast slab is cooled in each cooling process of a cooling roll and a reduction cooling roll.