JPH02220736A - Continuous casting method and mold for continuous casting - Google Patents

Abstract

PURPOSE:To produce a cast slab having stable surface property without using powder, etc., by sticking ceramic to an inner wall face in a copper-made mold, varying the thickness step by step and starting the solidification of molten metal at a part lower than molten metal surface part. CONSTITUTION:The mold 1 for continuous casting is composed of the copper- made mold body 2 having good thermal conductivity and a cooling box 3 providing a cooling water piping 4, and the poured molten metal 5 is cooled, solidified and drawn to the arrow mark P direction. Then, in the inner wall face of the mold body 2, the ceramics 6a-6d are stuck so as to go to thinner step by step toward the casting direction P, and as the ceramic, BN, Si3N4, graphite, etc., are used. By this method, the poured molten metal 5 is slowly cooled and the solidification starts from solidified starting point at the part lower than the molten metal surface 8, and the solidified shell 7 having stable surface property without influencing any variation of the molten metal surface 8, is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a continuous casting method and a continuous casting mold for producing slabs free of defects such as oscillation marks.

[Conventional technology]

Molten metal such as molten steel poured into a mold for continuous casting is cooled and solidified by heat removal through the mold, and is sent out as a high-temperature slab. Figure 9 shows the solidified shell formation and
It is a figure explaining a growth process. That is, the mold 51
The molten metal 52 poured into the mold 51 is heated and cooled by cooling water 54 flowing through a cooling water pipe 53 built into the mold 51.

Then, a solidified shell 55 is generated and grown at a location in contact with the inner wall of the mold 51. At this time, powder 56 is spread over the molten metal 52 to protect the molten metal surface from the oxidizing atmosphere. The powder 56 enters between the inner wall surface of the mold 51 and the solidified shell 55 as a part of the slag 57, and improves the lubricity of the solidified shell 55. The formed solidified shell 55 solidifies and contracts as it moves down the mold 51, and is sent out as a slab from the continuous casting mold 51 while enlarging the air gap 58 between it and the inner wall surface of the mold 51.

When performing continuous casting using the powder 56, the mold 51 is vibrated so that the powder 56 is fed along the inner wall surface of the mold 51. However, this vibration generates oscillation marks on the solidified shell 55, and the powder 56 is caught in the oscillation marks, causing surface flaws.

Also known is a mold for continuous casting in which a low thermal conductivity material such as ceramics is attached to the inner wall surface. For example, a mold with a low thermal conductivity material pasted thereon is one in which a low thermal conductivity material is pasted to the lower end or halfway of the mold 51 including the meniscus in order to slowly cool the molten metal 52 or the solidified shell 55. Japanese Patent Publication No. 58-17306
This method has been proposed in Publication No. 1, Japanese Unexamined Patent Publication No. 1987-195742, and the like. In addition, in order to extend the life of the mold 51, it is possible to apply a wear-resistant material such as ceramics or stainless metal to the inner wall surface of the mold 51, including the vicinity of the lower end.
This is proposed in Japanese Patent Application Laid-Open No. 13433/1983.

[Problem to be solved by the invention]

I mentioned JP-A No. 58-173061, vf Kai-Sho 6
In the mold proposed in Publication No. 1-195742, etc., solidification starts from the surface of the molten metal. Therefore, powder 56 is required, and problems such as oscillation B marks and powder entrainment remain unsolved. Furthermore, the wear-resistant material disclosed in JP-A-58-13413 is used to protect the lower end of molds used in high-temperature atmospheres, and is used to protect against solidification of poured molten metal. does not have any particular impact. Therefore, in this case as well, problems such as oscillation marks and powder entrainment remain unsolved as in the case of using conventional molds.

Therefore, the present invention enables submerged solidification by changing the thickness of the low thermal conductivity material attached to the inner wall surface of the mold in the casting direction, thereby achieving excellent surface quality without the need to use powder for lubrication. The purpose is to manufacture slabs with

[Means to solve the problem]

In order to achieve the objective, the continuous casting method of the present invention attaches ceramics to the inner wall surface over the entire length of the copper mold body, changes the thickness of the ceramics stepwise or continuously along the casting direction, and melts the ceramics. It is characterized by starting the solidification of metal below the surface area. In addition, a tundish is directly connected to a mold in which ceramics whose wall thickness is changed sequentially along the casting direction is attached to the inner wall surface, and molten metal is supplied from the tundish into the mold and solidified by heat removal through the inner wall of the mold. It is also possible to generate and grow shells.

In addition, the continuous casting mold for this purpose is made by pasting ceramics on the inner wall surface of a copper mold, changing the thickness of the ceramics stepwise or continuously along the casting direction, and contacting the molten metal at the surface of the hot water. The topmost ceramic is so thick that the molten metal starts to solidify below the surface area. A mold for continuous casting in which friction is released when the solidification of the molten metal starts below the molten metal surface and the mold is tapered in consideration of the static pressure of the molten steel at a height of the molten metal above the solidification point. becomes. Alternatively, a split type tiled structure with staggered joints may be used as the ceramic lining.

[Effect]

FIG. 1 shows the basic structure of a continuous casting mold according to the invention. This continuous casting mold 1 includes a copper mold body 2 with good thermal conductivity and a cooling box 3 provided on the back side of the mold body 2.
It is equipped with The cooling box 3 is provided with a cooling water pipe 4, and the cooling water flowing through the cooling water pipe 4 cools and solidifies the molten metal 5 poured into the continuous casting mold 1. Further, ceramics 6b to 6d having different thicknesses are attached to the inner wall of the copper mold body 2 along the casting direction indicated by the arrow P. Nafu, top ceramics 6a
is placed on the upper surface of the copper mold body 2 with sufficient wall thickness, and acts as a heat insulating layer.

As these ceramics 6a to 6d, boron nitride (BN), silicon nitride (SisN4), graphite, or the like having excellent lubricity is used. By pasting the ceramics 6b to 6d on the inner surface of the copper mold body 2,
This prevents the solidified shelf formed by solidifying the molten metal 5 from sticking to the inner wall surface of the continuous casting mold 1, or in extreme cases, from breaking the solidifying shelf and causing melt leakage. In addition, since it is no longer necessary to use powder to lubricate between the inner wall surface of the continuous casting mold 1 and the solidification shelf as in the past, powder entrainment caused by fluctuations in the molten metal level can be avoided.
Furthermore, defects such as surface flaws do not occur. however,
In the operating state, powder as a lubricant is not necessary, but as shown in FIG.
7 is used.

When lining the copper mold body 2 with ceramics, due to the excellent lubricity of the ceramics 6b to 6d,
The slab can be pulled out smoothly. Therefore, the slab is free from defects and has a clean casting surface.

The ceramics 6b to 6d arranged on the inner surface of the copper mold body 2 prevent the molten metal 5 from coming into direct contact with the copper mold body 2, and act as a heat insulating layer to slowly cool the molten metal 5 or the solidified shelf. Therefore, the amount that the solidified shelf has shrunk within 1° of the continuous casting mold can be recovered by creep, and the shrinkage of the shell due to rapid cooling and solidification can be prevented between the inner wall surface of the continuous casting mold 1 and the solidified shelf. There is no air gap. As a result, a uniform solidified shell thickness is produced, allowing high speed drawing of the slab.

When the ceramics 6h to 6d are provided on the inner wall surface of the continuous &jj-molding protective mold in this way, the amount of heat transferred through the wall surface changes along the casting direction P as shown in FIG. In other words, since the thick-walled uppermost ceramic 6a is placed at the top of the continuous casting mold l, the heat removal capacity of this part is
is almost negligible. By changing the wall thickness according to the ceramics 6a→6d, it is also possible to change the heat removal capacity depending on the operation.

For example, when casting ordinary steel, as shown in line [a] in Figure 2, in order to make the conventional heat removal pattern uniform, the wall thickness is changed according to ceramics 6a → 6d to remove heat during initial solidification. Strengthen the capacity and gradually reduce the heat removal capacity. This is a method equivalent to conventional powder casting, and is the most common heat removal pattern within the range of conventional operations.

In addition, the line ) indicates a heat removal pattern depending on the type of steel that requires slow cooling for low-speed casting, such as when casting alloy steel such as chromium-based stainless steel.
→The wall thickness decreases according to 6d, and the heat removal capacity gradually increases. Alternatively, it has been found that a pattern with a constant heat removal capacity like line (C) is effective for slow cooling in high-speed casting. The cooling pattern of line (C) is obtained by increasing the thickness of the ceramics 6b to 6d from the upper end of the mold downward. In any of these patterns, the molten metal 5 poured into the continuous casting mold 1 starts to solidify from a solidification start point 9 located below the molten metal level 8.

As a result, the generated solidified shelf has stable surface properties without being affected by fluctuations in the hot water level 8. Preferably, a pattern for obtaining solidification and shrinkage suitable for the type of steel to be cast is determined, and the taper is set in accordance with that pattern for operation.

The thickness of the solidification shelf is determined by the casting direction P of the continuous casting mold 1.
It gradually increases in size in response to changes in the heat removal capacity along the curve, and can create a state in which it is always in contact with the inner wall surface of the continuous casting mold 1. In the conventional powder casting method, the flow of powder is not uniform and may be interrupted, so that the solidified shell contracts due to partial strong cooling, creating an air gap. This tendency becomes more pronounced as it approaches the lower end of the continuous casting mold 1. but,
In the present invention, a state in which the powder flows uniformly is artificially created, and the solidification shelf does not come into direct contact with the copper mold body 2, so the solidification shelf always remains in the continuous casting mold 1.
Fits on the inner wall surface of the

Furthermore, the thickness of the ceramic is increased in the upper part of the continuous casting mold 1 which is exposed to high temperatures, and is made thinner in the lower part where the surface temperature is relatively low. Therefore, ceramics 6b to 6d
The temperature at the back surface of the copper mold body 2 is lowered overall, and the adhesive for attaching the ceramics 6b to 6d to the inner wall surface of the copper mold body 2 is not exposed to high temperatures and deteriorated.

On the other hand, in the conventional mold, its heat removal capacity changes into an S-shaped curve due to the formation of an air gap, as shown by the curve in FIG. Then, the molten metal 5 is cooled from just below the hot water level 8, and a solidification shelf is formed. This rapid formation and growth of the solidified shelf causes contraction, and the air gap described in FIG. 9 is likely to occur between the mold 1 for continuous casting and the inner wall surface. Therefore, the heat removal capacity is significantly reduced.

In this case, the air gap can be reduced by increasing the drawing speed of the slab. However, there is a limit to increasing the drawing speed because it causes breakage of the powder film, an increase in frictional resistance, etc., and the drawing speed cannot be increased too much.

In this way, when using the continuous casting mold 1 having the ceramics 6b to 6d inside, the molten metal 5 and the solidification shelf are slowly cooled, and a slab with good surface quality is obtained. In addition, since the lubrication of the solidification shelf for the ceramics 6b to 6d is excellent, it is not necessary to use a lubricant such as powder (when the slab is pulled out from the continuous casting mold 1. Therefore, the slab obtained is , there will be no surface defects caused by powder entrainment or oscillation marks.Furthermore, since the formation of the solidified shelf starts at a position below the hot water level 8, it will not be affected by hot water level fluctuations. A slab with stable surface properties can be obtained.

Ceramics 6a provided on the upper part of the continuous casting mold 1
And the ceramics 6b to 6d provided on the inner wall surface can be fixed by means as shown in FIG. That is, the uppermost ceramic 6a is pressed against the upper surface of the copper mold body 2 by the clamp 10. Further, the ceramics 6b to 6d on the inner wall surface are attached to the inner surface of the copper mold body 2 with a ceramic adhesive 11. At this time, the ceramics 6b to 6d may shift downward due to the frictional force F generated between the solidification shelf and the inner wall surface of the continuous casting mold 1 as the slab is pulled downward. Therefore, as shown in the figure, a step is provided in the copper mold body 2, and the individual ceramics 6b to 6b are separated from each other at this step.
It is better to support the lower end of 6d.

In addition, in order to smoothly lubricate between the ceramics 6b to 6d and the solidification shelf in subsurface solidification in which the solidification start point 9 is below the hot water level 8, a taper with an appropriate angle with respect to the vertical line is used. is preferably provided on the inner surfaces of the ceramics 6b to 6d. FIG. 4 shows an appropriate pattern when considering the static pressure of molten steel during subsurface solidification. H
5 is the distance index from the solidification start point 9 (meniscus) to the hot water level 8, and Tt is the number of ceramic chiefs M provided on the inner wall surface of the mold in the range from the upper end of the mold to the lower end of the mold (assuming the vertical state is 0, When defined as (indexed), the relationship with the optimal taper index T+ in consideration of friction is in the shaded area. That is, when the distance index H1 is large and a large molten steel static pressure is applied, the taper index TI is increased to the negative side and the inner wall surface is opened downward. On the other hand, when the distance index H1 is small, the taper index Ti
to the positive side, that is, the inner wall of the mold is opened upward,
Grow a solidification shelf.

This is because the initial solidification strength is weak, so in order to prevent the shell from breaking, the mold taper must be set in the casting direction P under conditions that do not impair the cooling conditions. The purpose of this is to relieve the friction caused by the static pressure of molten steel. Another purpose is to reduce the increase in friction caused by the molten steel head when the tandem shell and the continuous casting mold 1, which will be described later, are connected. Moreover, this taper adjustment has the great effect of reducing the lubrication resistance of the continuous casting mold 1 and enabling high-speed casting despite solid lubrication.

In FIGS. 1 to 3, a plurality of ceramics 6b to
6d is provided on the inner wall surface of the continuous casting mold 1. For the construction of ceramics on the continuous casting mold 1, it is conceivable that the ceramic be laminated in an integrated form such as a break ring of a horizontal continuous casting machine. However, large-sized ceramics are difficult to manufacture and install.
This imposes major restrictions on usage. Therefore, in order to apply it to a vertical continuous casting mold, it is preferable to have a subdivided tiled structure as shown in FIG. In addition, Figure 5 (
Figure a) shows a variable type continuous casting mold, and Figure 5) shows a fixed type continuous casting mold. In either example, ceramics are arranged as small pieces a in a staggered manner on the inner surface of the copper mold body 2, and constitute the inner wall surfaces of the long side 1a and the short side 1b. Compared to the fact that the current powder-based lubrication system itself is partially uneven and the overall contact area ratio is only about half, the effect on heat removal characteristics when using this tiled structure is It is very good.

When the ceramic pieces a are arranged in a staggered manner, it is expected that the unevenness of the joints between the tiles will inhibit the formation of a solidified shell. However, as shown in FIG. 6, experimentally, by setting the horizontal distance C between the ceramic pieces 3 and the joint f to 0.5 mfil or less, a sound and solid shell was obtained without any problem.

However, the form of the ceramic is not limited to this, and an integral ceramic member 6 may be provided on the inner wall surface of the continuous casting mold 1 as shown in FIG. This ceramic member 6 has a thick wall in a portion near the molten metal level 8, and the wall thickness is continuously reduced in a lower portion.

In this way, by making the uppermost ceramic in contact with the molten metal 5 near the molten metal surface 8 thick, the starting point 9 between the V surfaces
can be taken below the hot water level 8, and coagulation below the hot water surface is performed. Therefore, by taking advantage of this subsurface solidification, it becomes possible to connect the mold directly to the tandem dish.

FIG. 8 shows an equipment configuration using the above-mentioned continuous casting mold. Molten gold scraps 5 are supplied to the tandem dish 12 from a long nozzle 13. The molten metal 5 is poured into the continuous casting mold 1 through a sliding nozzle 14 provided on the bottom wall of the tundish L12.

FIG. 8(a) shows an example equipped with a continuous casting mold 1 whose width can be changed, for example, when manufacturing a slab material. In this example, since the tundish 512 and the continuous casting mold 1 are directly connected, the upper part of the continuous casting mold 1 is covered with the cover 15 without being opened as in the conventional case. Note that the continuous casting mold 1 can be slid in the direction of the arrow in a positional relationship in which the short side 1a of the mold is perpendicular to the cover 15. At this time, since the ceramic 6 having excellent lubricity is placed on the upper part of the continuous casting mold 1, the continuous casting mold 1 slides smoothly with respect to the cover 15.

Figures 8 and 8) show an example in which a continuous casting mold 1 with a fixed width is incorporated, such as when manufacturing bloom material, and the pouring ports of the continuous casting mold 1 and the tundish 512 are thickened (or The openings are the same.This allows casting without a nozzle restriction or the like.

In this way, a solidification shelf can be generated without exposing the molten metal 5 to be cast to the atmosphere, so that the problem of oxidation of the molten metal surface is completely eliminated. Further, when the opening degree of the sliding nozzle 14 is appropriately selected, the static pressure applied to the molten metal 5 in the continuous casting mold 1 is also controlled, and defects such as breakouts do not occur. Note that it is also possible to adjust the static pressure by winding an electromagnetic coil around the sliding nozzle 14 and applying an upward driving force to the molten metal flow flowing through the sliding nozzle 14.

On the other hand, in the conventional casting method, molten steel is injected into the continuous casting mold 1 from the bottom wall of the tundish 12 through a nozzle, and is cooled and solidified using a copper plate mold. Therefore, the melt level is the starting point for solidification, and powder is used as a lubricant between the copper plate and the solidified shell. Therefore, powder and Al2O3 in the mold
The problem of entrainment of system inclusions is accompanied by serious quality problems in the Ti industry, such as bubble defects and clogging of the immersion nozzle due to the entrainment of sealing argon gas and air from the split type immersion nozzle.

Therefore, in order to solve these problems, ■ do not use powder; ■ do not use the melt level as the starting point for solidification; and ■ have a vertical section of 2.5 m or more in length to promote the floating of inclusions. (2) It is necessary to have a large-hole injection pipe in place of the immersion nozzle. In order to fundamentally improve this problem, it is effective to connect the tandate shoe mold directly.

By directly connecting the tundish and the mold, the control parts of the casting process, such as injection amount control, molten metal level, and powder addition, which were previously considered extremely difficult, are reduced and the work is simplified. This makes it possible to completely automate the casting process, resulting in significant labor savings. Furthermore, since a large-hole injection pipe is required in place of the immersion nozzle, defects caused by inclusions such as powder and slag that occur in the continuous casting mold when using conventional methods are prevented.

Furthermore, it is possible to enlarge the joint opening between the tundish and the continuous casting mold, which prevents nozzle clogging and enables low-temperature casting.By improving segregation and lowering the melting temperature, costs, especially for refractories, can be significantly reduced. can be reduced. In addition, by directly connecting the tundish and the continuous casting mold, even a curved continuous casting machine can have a vertical section, and has the function of a vertical bending continuous casting machine. As described above, the present invention brings about many effects.

〔Example〕

A copper mold body 2 of a continuous casting mold l having an internal space with a cross section of 250 mm x 250 mm has a thickness of 12 mm.
A BN block of zero weight was placed as the uppermost ceramic 6a, and was pressed and fixed to the upper surface of the continuous casting mold 1 with a clamp 10. In addition, the ceramics 6b to 6d to be attached to the inner wall surface of the copper mold body 2 have thicknesses of 11 mm, 9 mm, and 7 mm, respectively, and lengths in the casting direction P of 20011111.200 mm and 300 IIl.
+a BN block was used.

This continuous casting mold 1 has a common steel composition and has a temperature of 154
Molten steel at 0°C was injected, and a slab with a wall thickness of 250 m1b and a plate width of 250 mm was cast at a casting speed of 0.9 m/min. At this time, when the temperature of the copper plate measured by the thermocouple was analyzed using the finite element method, the solidification starting point 9 was found to be
It was at a position 50 stops below the hot water level 8. The obtained slab had good surface properties with no surface flaws or creases.

In addition, as shown in FIG. 8, when similar molten steel was poured into the tundish 512 directly connected to the continuous casting mold 1 for casting, slabs with similarly excellent surface properties were obtained. At this time, the molten steel flowing down from the tundish 12 did not come into contact with the atmosphere, so it had the same cleanliness as the molten steel injected into the tundish x12, and had an internal structure without entrainment of oxides.

〔Effect of the invention〕

As explained above, in the present invention, the inner wall surface of the copper mold body is lined with ceramics, and this ceramic layer is made thin along the casting direction. Therefore, the molten metal and the solidified shell are slowly cooled, and the lubrication of the solidified shell produced in the mold is improved. In addition, by combining it with a friction open mold, there is no need to use powder or apply vibration to the mold.
Continuous casting can be performed and slabs with excellent surface properties can be obtained. Moreover, since sub-surface solidification is possible, defects caused by fluctuations in the surface of the molten metal at the meniscus do not occur in the solidified shell, and casting can be performed with the mold itself directly connected to the tundish.

[Brief explanation of the drawing]

Fig. 1 shows the basic structure of the continuous casting mold according to the present invention, Fig. 2 is a graph of the heat removal capacity of the mold viewed in the casting direction, and Fig. 3 shows the basic structure of the continuous casting mold according to the present invention. Figure 4 shows the relationship between molten steel static pressure and mold taper, Figure 5 shows the inner wall of the copper mold body lined with ceramic pieces, Figure 6 shows the allowable smoothness of the joints, Figure 7 shows a continuous casting mold lined with integral ceramics, and Figures 8 (a) and (c) are views of the continuous casting mold directly connected to the tandem shell, viewed from the long and short sides of the mold, respectively. It is. On the other hand, FIG. 9 shows a state in which casting is performed using a conventional continuous casting mold. 1: Continuous casting mold 2: Copper mold body 3; Cooling box 4: Cooling water piping 5; Molten metal p
6.6a to 6d: Ceramics 7: Solidification shell 8: Molten metal surface 9: Solidification start point 10: Clamp 11: Ceramic adhesive 12: Tandish I3: Long nozzle 14 Varnish sliding nozzle P: Casting direction F: Friction force

Claims (1)

[Claims] 1. Pasting ceramics on the inner wall surface of a copper mold,
A continuous casting method characterized in that the thickness of the ceramic is changed stepwise or continuously along the casting direction, and solidification of the molten metal is started below the molten metal level. 2. Paste ceramics on the inner wall of the copper mold,
The thickness of the ceramic is changed stepwise or continuously along the casting direction, and the topmost ceramic that is in contact with the molten metal at the hot water level is set such that solidification of the molten metal starts below the hot water level. A continuous casting mold characterized by its thick wall thickness. 3. Using a mold in which ceramics whose wall thickness is changed sequentially along the casting direction is attached to the inner wall surface, the tundish and the mold are connected via a heat insulating material, and the molten metal is poured into the mold. A continuous casting method characterized by producing and growing a solidified shell by supplying heat and removing heat through the inner wall of the mold. 4. Paste ceramics on the inner wall of the copper mold,
The thickness of the ceramic is changed stepwise or continuously along the casting direction, and the topmost ceramic that is in contact with the molten metal at the hot water level is set such that solidification of the molten metal starts below the hot water level. In this mold, a friction open type continuous casting mold is provided with a mold taper that takes into consideration the static pressure of molten steel at a height above the solidification point. 5. Paste ceramics on the inner wall of the copper mold,
In a mold in which the thickness of the ceramic is changed stepwise or continuously along the casting direction so that the solidification of the molten metal starts below the molten metal surface, the ceramic pieces are divided into pieces in a staggered pattern. A continuous casting mold characterized by being attached to the inner wall of a copper mold body.