JP4102316B2 - Method for continuous casting of molten metal - Google Patents

Description

  The present invention relates to a molten metal continuous casting method for improving the surface properties of a slab by applying electromagnetic force to molten metal in a mold to suppress instability of initial solidification.

Normally, in continuous casting of molten metal, a lubricant powder (hereinafter sometimes referred to as “powder”) is provided on the surface of the molten steel in order to provide the required lubricity between the mold wall and the solidified shell. Added. The melted powder flows into the gap between the mold wall and the solidified shell by the relative movement of the mold wall that vibrates up and down and the solidified shell that is pulled out at a constant speed.
The meniscus and the tip of the solidified shell are deformed by the dynamic pressure generated during the inflow. This deformation is repeated at the mold oscillation cycle to form an oscillation mark (periodic flaw) on the surface of the slab. Contributes to stabilizing the surface quality of the slab.

In order to ensure the surface quality of the slab, it is necessary to eliminate instability in the initial solidification of the molten metal and ensure lubricity between the mold and the solidified shell, and various methods and apparatuses for this purpose have been proposed. Yes.
For example, in (Patent Document 1), in a continuous casting method in which molten metal is poured into a water-cooled mold that vibrates with a lubricant at a constant cycle, and a slab is continuously drawn downward, an electromagnetic coil provided around the mold is used. A method of improving the surface properties of a slab by continuously energizing an alternating current and using the generated electromagnetic force to raise the molten metal in the mold in a convex shape is described.

Further, (Patent Document 2) discloses that when electromagnetic force is applied to molten metal in a mold by an electromagnetic coil, the electromagnetic force is intermittently applied by applying an alternating magnetic field, and powder between the solidified shell and the mold wall is applied. Describes a method of further promoting the flow of water and improving the surface properties.
Further, in Patent Document 3, an alternating current is applied to a solenoidal electromagnetic coil arranged so as to surround a continuous casting mold or a solenoidal electromagnetic coil embedded in a side wall of the continuous casting mold to start solidification. A method for improving the surface quality of a slab is described by continuously casting an electromagnetic force on the molten metal while applying an electromagnetic force in a direction away from the mold wall.

Further, in (Patent Document 4), in a method of performing continuous casting while applying AC electromagnetic force by an electromagnetic coil in the vicinity of a molten steel meniscus, a molten metal injection nozzle having a discharge port opened in a downward direction is provided. A method is described in which the surface properties of the slab are improved by disposing it in the mold so as to be positioned below the center of the electromagnetic coil.
JP 52-32824 A JP-A-64-83348 International Publication WO 96/05926 JP-A-11-188460

  In the methods of (Patent Document 1) to (Patent Document 3) described above, the surface properties may be improved, but the discharge of the molten metal injection nozzle with respect to the distribution of electromagnetic force in the casting direction in the mold. If the holes are not in the proper range, the flow of molten metal injected from the molten metal injection nozzle interferes with the flow of molten metal induced in the molten metal by electromagnetic force, and the flow of molten steel in the mold becomes unstable. Disturbances may occur in the molten metal meniscus, and the improvement in the surface properties of the slab becomes non-uniform in the circumferential direction of the mold, and the powder is caught in the molten steel at the meniscus and trapped in the solidified shell, resulting in slab defects It became clear that there was a problem of becoming.

  Further, as in the method of (Patent Document 4), a molten metal injection nozzle having a discharge port that opens downward is disposed in the mold so that the discharge port is positioned below the center of the electromagnetic coil. This suppresses the influence of the flow turbulence caused by the interference between the discharge flow from the molten metal injection nozzle and the flow of the molten metal induced in the molten metal by electromagnetic force on the meniscus, and the molten steel in the mold It tends to stabilize the flow.

  However, since the discharge port of the molten metal injection nozzle opens in the downward direction, interference with the flow of molten metal induced in the molten metal by electromagnetic force can be suppressed, but the speed of the downward molten steel flow is large Therefore, the molten steel flow in the mold tends to be non-uniform. In addition, there is a limit to the immersion depth of the nozzle, etc., and since the molten steel discharge flow is formed at a position away from the meniscus, it becomes difficult to supply the sensible heat of the molten steel to the initial solidification part, improving the slab surface properties There is also a problem that is difficult to achieve.

  The present invention relates to a method for continuously casting a slab from molten metal, and stabilizes the molten metal meniscus behavior by changing the immersion depth of the molten metal injection nozzle according to the distribution of magnetic flux density in the casting direction in the mold. An object of the present invention is to provide a casting method capable of stably obtaining a lubrication improving effect and a slab surface property improving effect.

The gist of the present invention is as follows.
( 1 ) AC current is applied to the solenoid type electromagnetic coil arranged so as to surround the mold or the solenoid type electromagnetic coil embedded in the mold wall, and electromagnetic force is applied to the molten metal in the mold to change the meniscus shape. In the continuous casting method of molten metal that is cast while the position where the magnetic flux density in the casting direction in the mold is maximum is shifted upward from the center position of the electromagnetic coil, the position of the discharge hole of the molten metal injection nozzle is A method for continuously casting molten metal, characterized by adjusting the magnetic flux density in the casting direction in the mold to a range below the position where the maximum value is reached and to the center position of the electromagnetic coil .
( 2 ) Use of a molten metal injection nozzle having two holes for discharging molten metal from the opposite mold wall surface direction to the vertically downward direction, and an angle formed by the center line of each hole and the horizontal plane being 60 degrees or less. The continuous casting method of molten metal as described in (1) .
( 3 ) The molten metal continuous casting method according to (1), wherein a molten metal injection nozzle including a slit portion that is discharged from a vertically downward direction directly below the nozzle toward a facing mold wall surface is used.
( 4 ) Two holes are provided to discharge molten metal from the opposite mold wall surface direction to the vertically downward direction, and the angle between the center line of each hole and the horizontal plane is 60 degrees or less, and further vertically below the nozzle. (1) The molten metal continuous casting method according to (1), wherein a molten metal injection nozzle that continuously includes a slit portion that is discharged from a direction toward a facing mold wall surface is used.
( 5 ) The molten metal continuous casting method according to any one of (1) to (4) , wherein oil is supplied to the meniscus of molten metal from the upper part of the mold.
(6) The continuous casting method of molten metal according to any one of (1) to (5) , wherein an alternating current supplied to the electromagnetic coil is periodically changed.
(7) The molten metal continuous casting method according to any one of (1) to (6) , wherein the alternating current supplied to the electromagnetic coil is periodically changed without vibrating the mold.

  According to the present invention, it is possible to prevent the powder from being caught in the molten steel at the meniscus portion, captured by the solidified shell, and becoming a slab defect. Therefore, the continuous casting has excellent surface properties and no casting defects. It is possible to produce a slab at high speed.

In order to solve the above problems, the inventors focused on the distribution of the magnetic flux density in the casting direction in the mold and the immersion depth of the molten metal injection nozzle, and conducted an intensive investigation on the relationship between the quality of the surface properties of the slab. Studied.
As a result, it was found that the position where the magnetic flux density in the casting direction in the mold becomes the maximum value and the center of the electromagnetic coil do not coincide with each other, and the position where the magnetic flux density becomes the maximum value and the position of the discharge hole of the molten metal injection nozzle. Has been found to have an appropriate relationship that can stably obtain the lubrication improving effect and the slab surface property improving effect.

The present invention is described in detail below.
The inventors pay attention to the distribution of the magnetic flux density in the casting direction in the mold, and the basic idea is to adjust the position of the discharge hole of the molten metal injection nozzle according to the distribution of the magnetic flux density. That is, since the electromagnetic force works at a position where the magnetic flux density becomes the maximum value, the discharge flow from the molten metal injection nozzle and the electromagnetic force are adjusted by adjusting the position of the discharge hole of the molten metal injection nozzle below this position. Therefore, the flow of the molten metal induced in the molten metal does not interfere.
Therefore, as described above, since the position where the magnetic flux density in the casting direction in the mold becomes the maximum value and the center of the electromagnetic coil do not coincide with each other, the position of the discharge hole of the molten metal injection nozzle is based on the position where the magnetic flux density becomes the maximum value. It is important to set
Further, when the distribution of the magnetic flux density in the casting direction in the mold was investigated, it was found that the position where the magnetic flux density reached the maximum value was usually shifted upward or downward from the center position of the electromagnetic coil.

A specific example of the present invention will be described with reference to FIG. 1 in the case where the position where the magnetic flux density is maximum is shifted upward from the center position of the electromagnetic coil.
In FIG. 1, an alternating current is applied to a solenoid type electromagnetic coil 4 arranged so as to surround the mold 3, and electromagnetic waves are supplied to the molten steel 5 supplied into the mold as a molten steel discharge flow 8 a from the tundish 1 through the molten metal injection nozzle 2. A mode of continuous casting is shown in which the force 9 is applied to change the molten steel meniscus shape 10a in the mold, and the solidified shell 6 is pulled out while casting while the powder 7 is supplied. Moreover, the stirring flows 11a and 12 are induced in the molten steel by the electromagnetic force 9.
At that time, based on the distribution of the magnetic flux density in the casting direction in the mold, the upper end 14 of the discharge hole of the molten metal injection nozzle is adjusted downward from the position 15 where the magnetic flux density becomes the maximum value. Since the discharge flow 8a and the stirring flow 11a do not interfere with each other, the molten steel meniscus shape 10a in the mold is stably maintained, and the lubrication improving effect and the slab surface property improving effect can be stably obtained in the mold circumferential direction. The position of the discharge hole of the molten metal injection nozzle can be implemented by adjusting the immersion depth of the molten metal injection nozzle.

  On the other hand, as shown in FIG. 2, when the upper end 14 of the discharge hole of the molten metal injection nozzle is above the position 15 at which the magnetic flux density in the casting direction in the mold becomes the maximum value, the molten steel discharge flow 8b and the stirring flow 11b are The molten steel meniscus shape 10b in the mold becomes unstable due to interference, and the lubrication improving effect and the slab surface property improving effect cannot be stably obtained in the mold circumferential direction.

Further, the position 15 at which the magnetic flux density becomes the maximum value is above the center position 16 of the electromagnetic coil. In this situation, the position of the discharge hole of the molten metal injection nozzle may be adjusted to any position as long as it is below the position 15 at which the magnetic flux density becomes the maximum value. Therefore, restrictions such as the position of the discharge port of the molten metal injection nozzle and the immersion depth of this nozzle are relaxed and can be set relatively freely. There is an advantage that the range of selection of the nozzle setting position when the nozzle is moved up and down appropriately is widened.
Further, when the position of the discharge hole of the molten metal injection nozzle is set to a range below the position 15 where the magnetic flux density is maximum and to the center position of the electromagnetic coil, the sensible heat of the molten steel is supplied to the initial solidification part. This is preferable because it tends to improve the slab surface properties.

  On the other hand, if the position where the magnetic flux density reaches the maximum value is shifted downward from the center position of the electromagnetic coil, the position where the magnetic flux density becomes the maximum value is regarded as the center position of the electromagnetic coil as in the prior art. If the coil is disposed at the center position of the coil, flow disturbance due to interference between the discharge flow from the molten metal injection nozzle and the flow of the molten metal induced in the molten metal by electromagnetic force occurs. However, as in the present invention, by setting the nozzle position based on the position where the magnetic flux density becomes the maximum value, the disturbance of the flow due to such interference can be prevented.

In the present invention, various molten metal injection nozzles can be used.
As one form thereof, a molten metal injection nozzle having two holes for discharging molten metal from the opposite mold wall surface direction to the vertically downward direction, and an angle θ between the center line of each hole and the horizontal plane being 60 degrees or less. Is mentioned. The reason why the two holes are in the opposite directions is that a symmetric flow can be formed and a stable flow can be achieved.
In addition, if possible in construction, it may be provided with a plurality of holes (three or more holes) so as to discharge in a direction in which a symmetric flow can be formed, and is set appropriately in consideration of cost and labor. Is.

  In addition, the flow in the mold casting direction can be suppressed by setting the angle formed by the center line of each hole portion to the horizontal plane to be 60 degrees or less, so that the sensible heat of the molten steel is supplied to the initial solidification portion, and the slab surface property is Improved. When using a nozzle in which the center line of each hole has an angle with respect to the horizontal plane, it is important that the upper end of the discharge hole of the nozzle is located below the position where the magnetic flux density is maximum. is there.

  As another form of the molten metal injection nozzle, there is a molten metal injection nozzle provided with a slit portion that discharges from a vertically lower direction directly below the nozzle to a facing mold wall surface direction. By making the slit portion in this way, it is possible to make the flow spread from the vertical downward direction directly below the nozzle to the opposite mold wall surface direction, so that the molten steel discharge flow rate can be reduced, and as a result, the flow should be uniform. Can do.

In addition, the two forms described above are used in combination to provide two holes for discharging the molten metal from the opposite mold wall surface direction to the vertically downward direction, and the angle between the center line of each hole part and the horizontal plane is 60 degrees or less. In addition, it is also possible to use as a molten metal injection nozzle that is continuously provided with a slit portion that is discharged from the vertically downward direction directly below the nozzle toward the opposite mold wall surface. This hole part may be provided with a plurality of (three or more holes) hole parts as described above.
With this nozzle, the sensible heat of the molten steel is supplied to the meniscus portion to the initial solidification portion, the slab surface properties are improved, the molten steel discharge flow rate can be reduced, and a uniform flow can be achieved.

  Further, oil may be supplied to the molten metal meniscus from the upper part of the mold. Any oil may be used as long as it has heat and lubricity on the meniscus after being supplied to the meniscus. For example, Repseed oil can be used as a substitute for powder. Such oil supply improves the lubrication between the mold wall and the solidified shell and enables casting without the use of powder. For example, it can be used as needed, for example, for small-section molds. Just do it.

In addition, by periodically changing the alternating current that flows through the electromagnetic coil, the electromagnetic force also changes periodically, which stabilizes the flow of the molten steel, thereby improving lubrication between the mold wall surface and the solidified shell. Can be improved. The periodical variation width of the alternating current that is passed through the electromagnetic coil is not particularly specified, but it is usually preferable to carry out at about 2 to 20 Hz. If it is less than 2 Hz, the interval of the cycle becomes long, and if it exceeds 20 Hz, it approaches the state where it is continuously applied, so that the flow of molten steel is difficult to stabilize in any case.
In addition, since the molten steel can be heated by induction heating, the lubrication between the mold wall surface and the solidified shell can be further improved.

Furthermore, since the electromagnetic force periodically changes by periodically changing the alternating current supplied to the electromagnetic coil without vibrating the mold, the mold wall can be vibrated only by the change due to the electromagnetic force. it can. In this case, since the apparatus for vibrating the mold can be omitted, the apparatus can be simplified as a whole, and there is an advantage in terms of cost.
Further, similarly to the above, the molten steel can be heated by induction heating, and the lubrication between the mold wall surface and the solidified shell can be further improved.
In the present invention, means for improving the lubrication between the mold wall surface and the solidified shell as described above can be used in combination as appropriate.
Hereinafter, examples of the present invention will be described, but the conditions used in the examples are one condition example, and the present invention is not limited to these conditions.

An electromagnetic coil having a length of 1850 mm (long side) × 400 mm (short side) and a height of 200 mm was embedded in the mold, and continuous casting was performed under the following conditions.
In-mold dimensions: 900mm (long side) x 220mm (short side), height 800mm
Mold vibration stroke: 6mm,
Mold frequency: 120 cycles / min,
Casting speed: 1 m / min,
Hot water level: Upper end of coil (100 mm from upper end of mold),
Magnetic field condition: Single phase alternating current 200 Hz applied for 0.05 seconds and no applied for 0.05 seconds Also, a C—Ca—SiO ₂ —Al ₂ O ₃ —Na based powder was supplied as a lubricant, and a molten metal injection nozzle By changing the immersion depth, the position of the discharge hole of the molten metal injection nozzle was adjusted, and the molten steel of low carbon steel was continuously cast. As shown in FIG. 1, the molten metal injection nozzle was provided with two holes, and the angle between the center line of each hole and the horizontal plane was 30 degrees.

  The position (Ln) of the upper end of the discharge hole of the molten metal injection nozzle used, the coil center position, the position where the electromagnetic force in the casting direction in the mold becomes the maximum value (Lpe), the position where the electromagnetic force in the casting direction in the mold becomes the maximum value Table 1 shows the difference (Ln−Lpe) between the position of the upper end of the discharge hole of the molten metal injection nozzle and the position where the electromagnetic force in the casting direction in the mold becomes the maximum value. However, the starting point of measurement at each position is a molten steel meniscus.

The measurement result of the oscillation mark depth of the obtained slab surface is shown in FIG.
From FIG. 3, in the case of [1] and [2] where the position Ln of the upper end of the discharge hole of the molten metal injection nozzle is higher than the position Lpe where the electromagnetic force in the casting direction in the mold becomes the maximum value, When Ln−Lpe) is a negative value, there is a problem that the oscillation mark depth on the surface of the slab is large.
On the other hand, in the case of [3] and [4] where the position Ln of the upper end of the discharge hole of the molten metal injection nozzle is lower than the position Lpe where the electromagnetic force in the casting direction in the mold becomes the maximum value, that is, ( When Ln-Lpe) is a positive value, the depth of the oscillation mark on the surface of the slab can be reduced, and a good quality product is obtained.

It is a figure which shows the aspect of continuous casting. It is a figure which shows the aspect of continuous casting. It is a figure which shows the surface roughness of slab.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Tundish 2 ... Immersion nozzle 3 ... Mold 4 ... Solenoid electromagnetic coil 5 ... Molten steel 6 ... Solidified shell 7 ... Powder 8 ... Molten steel discharge flow 9 ... Electromagnetic force 10 ... Molten steel meniscus 11 ... Stir flow 12 ... Stir flow 13 ... Magnetic flux density 14 in the casting direction: Position 15 at the upper end of the discharge hole of the immersion nozzle 15 Position where the magnetic flux density in the casting direction is maximum 16 Position at the center of the solenoid type electromagnetic coil 17 Center line of the two holes of the immersion nozzle

Claims (7)

Casting while changing the meniscus shape by applying alternating current to the solenoid type electromagnetic coil arranged so as to surround the mold or the solenoid type electromagnetic coil embedded in the mold wall and applying electromagnetic force to the molten metal in the mold. In the molten metal continuous casting method to be performed, when the position where the magnetic flux density in the casting direction in the mold is maximum is shifted upward from the center position of the electromagnetic coil, the position of the discharge hole of the molten metal injection nozzle is set in the mold. A method for continuously casting a molten metal, characterized by adjusting the magnetic flux density in the casting direction to a range below a position where the magnetic flux density in the casting direction reaches a maximum value and to a center position of the electromagnetic coil . A molten metal injection nozzle having two holes for discharging molten metal from a facing mold wall surface direction to a vertically downward direction and having an angle formed by a center line of each hole and a horizontal plane being 60 degrees or less is used. Item 8. A molten metal continuous casting method according to Item 1 . 2. The molten metal continuous casting method according to claim 1, wherein a molten metal injection nozzle having a slit portion that is discharged from a vertically downward direction directly below the nozzle to a facing mold wall surface direction is used. It has two holes for discharging molten metal from the opposite mold wall direction to the vertically downward direction, and the angle between the center line of each hole and the horizontal plane is 60 degrees or less, and is further relative to the vertical downward direction directly below the nozzle. 2. The molten metal continuous casting method according to claim 1, wherein a molten metal injection nozzle that is continuously provided with a slit portion that is discharged toward the mold wall surface is used. The continuous casting method for molten metal according to any one of claims 1 to 4 , wherein oil is supplied to the meniscus of molten metal from the upper part of the mold. The method for continuously casting molten metal according to any one of claims 1 to 5 , wherein an alternating current supplied to the electromagnetic coil is periodically changed. The molten metal continuous casting method according to any one of claims 1 to 6 , wherein an alternating current supplied to the electromagnetic coil is periodically changed without vibrating the mold.

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