JPH0724921B2 - Subsurface solidification casting method in continuous casting - Google Patents

Description

TECHNICAL FIELD The present invention relates to a continuous casting method for slabs, blooms, billets and the like.

[Prior Art] Generally, in continuous casting, while rapidly lowering the solidified shell cooled by the mold on the inner wall of the mold,
It is important to grow the solidified shells in order to achieve sound solidification.

In order to achieve this sound solidification, a bath surface protective material is added to the upper part of the mold to prevent air oxidation of the molten metal and lubricate the solidified shell and the inner wall surface of the mold with molten powder to prevent baking and breakage of the solidified shell. is doing.

Further, in order to cool the mold and extend the life thereof, and to slowly cool the molten metal or the solidified shell, a low thermal conductive material is attached to the lower end or the middle of the mold including the solidification starting point. 58-173061, JP 61-1957
No. 42, etc. Further, in order to extend the life of the mold, it is possible to stick a wear resistant material such as ceramics or stainless steel on the inner wall surface including the vicinity of the lower end of the mold,
It has been proposed in Japanese Patent Laid-Open No. 58-14345, and has been partially put into practical use.

[Problems to be Solved by the Invention] However, in the above-described lubrication by molten powder using the surface protection material (so-called lubrication by melt), the uniformity of the molten powder flowing between the mold and the solidified shell is Is not obtained, the formation of the solidified shell becomes uneven. As a result, surface defects may occur due to baking of the solidified shell on the mold, breakage, or inclusion of powder.

Further, the above-mentioned JP-A-58-173061 and JP-A-61-19.
In the mold proposed in Japanese Patent Publication No. 5742, etc., solidification starts from the molten metal surface, so molten powder is required, and problems such as oscillation marks and powder entrainment remain unsolved. Further, the wear-resistant material disclosed in JP-A-58-13445 is used to protect the lower end of a mold used in a high-temperature atmosphere, and to prevent solidification of molten metal poured. Does not have any particular effect. Therefore, also in this case, the problems such as oscillation marks and powder entrainment still remain unsolved as in the case of using the conventional mold.

Therefore, the inventors of the present invention first proposed a casting method by solid lubrication by lining a small piece ceramics on the entire surface of the mold, and changing the thickness of the ceramics piece stepwise or continuously in the drawing direction of the cast piece. It is effective.

However, in order to solidify even solid lubrication casting in which this ceramic piece is lined under the molten metal surface, the solidified shell formed in the initial stage causes a peeling of the inner surface of the mold and a load for growth, and depending on the steel type (superheat amount), a metal bear In some cases, it may occur to hinder the formation and growth of solidified shells, and it is difficult to aim for high speed casting by solid lubrication.

From the above, according to the present invention, the inner wall surface of the mold is lined with ceramics, the ceramics are divided into small pieces, and the ceramics thickness is changed in the drawing direction of the cast piece to perform solid lubrication by the ceramics itself. An object of the present invention is to provide a continuous casting method capable of producing a slab of excellent quality at a high speed without solidifying below and using powder.

[Means for Solving the Problems] The present invention provides a continuous casting method in which a mold made of copper or plated on the copper surface is lined on the entire inner wall with the thickness of the small piece ceramics lined, and It is characterized in that the molten metal to be cast is heat-insulated, and subsequently, the molten metal is solidified below the molten metal surface through the inner curvature surface for cooling and solidifying the molten metal.

[Operation] The solidified shell produced during continuous casting is pressed against the lining ceramic piece by the static pressure of the molten metal, and when the slab is pulled out of the mold, a frictional force is generated between the slab and the ceramic lining. On the other hand, in the initial solidified shell just below the solidification start point, the thickness of the solidified shell is thin and weak. In order to prevent the slab from breaking due to the pulling force, it is necessary to reduce the frictional force by promoting solidification so that the solidified shell softly touches the ceramic lining surface. For this reason, in the vicinity of the solidification start point including the solidification start point of the ceramics lining, the inner surface of the mold has an inner curvature portion (hereinafter referred to as a rounded portion) having an arc angle of 90 degrees or less at the lower end and the upper end of the arc. It is effective to provide over the entire circumference of the inner peripheral surface. The solidified shell in contact with the radius portion has a force in the radius direction of the radius of the radius portion due to the slab withdrawal force,
In other words, the force of separating the solidified shell from the lining surface acts against the static pressure of the molten metal, and the frictional force acting on the solidified shell at the initial stage of solidification is reduced. This enables high speed solid lubrication casting within the fracture limit of the initially solidified shell.

The radius of curvature r of the rounded portion is appropriately 20 to 400 mm. If the radius of curvature is less than 20 mm, the heat removal capability will decrease with drawing and remelting or double solidification surface will occur. Further, the length of the frictional force releasing area becomes shorter, and the effect of reducing the frictional force becomes smaller. On the other hand, when the radius of curvature exceeds 400 mm, the solidified shell is pressed against the lining surface by the static pressure of the molten metal and passes through, and the effect of releasing the frictional force cannot be obtained. As a result, solidified shell fracture occurs, leading to breakout. The arc angle is
It is preferably 90 degrees to 3 degrees.

The extremely thin and fragile solidified shell formed by the initial solidification reduces the friction between the inner surface of the mold and the solidified shell due to the component force between the slab withdrawal direction and the radius of curvature of the rounded portion. There is nothing to do. As a result, sound solidification can be achieved by the continuous formation of the initially formed solidified shell and the subsequent normal cooling. Moreover, the generation of the metal bear due to the fluctuation of the molten metal surface during casting is suppressed by this curved portion.

As described above, the solidified shell initially formed by the action of this curved surface easily separates from the ceramic piece of the cooling part by the separation component force, and the upper end repeats remelting and formation of the solidified shell by the self-heating of the existing melt. The thickness of the solidified shell increases as it goes downward. As a result, the solidified shell is smooth and defect-free.

Further, in order to cause solidification under the molten metal surface, the solidification starting point is preferably at least 30 mm below the molten metal surface. If it is less than 30 mm, the heat insulating material sprinkled on the surface of the molten metal is caught in the molten metal, and it becomes difficult to solidify below the surface due to fluctuations in the surface of the molten metal. It becomes a defect solidification shell. At least 30 solidification points from the surface
The solidified shell produced by locating
It will have stable surface properties without being affected by fluctuations in the molten metal surface.

[Examples] Next, the case where the under-surface solidification casting method of the present invention is cast under the mold structure shown in FIG. 1 and the conditions shown in Table 1 will be described.

First, in the drawing, 1 is a copper mold, 2 is a cooling water flow path, and a ceramic piece 3 is bonded to the inner wall of the copper mold 1 with a layer in which an organic adhesive and metal powder are mixed. The thickness of the ceramic piece 3 is changed stepwise in the casting direction of the copper mold 1 (that is, the thickness is reduced in the drawing direction), and the heat insulating portion 5a of the molten metal and the cooling are formed on the upper end or the upper part of the copper mold 1. A ceramics 5 having an inner curvature surface 4 in which a portion 5b to be solidified is successively formed is arranged all around. Further, in the structure of the heat insulating portion, if the heat insulating space 11 is provided in order to allow the superheat amount to be low, the heat insulating portion 5a
It is possible to prevent the metal from being partially attached to the.

Molten metal 7 is injected from the dipping nozzle 6 into the mold thus configured, and solidification is performed from the solidification start point 8. No. 9 is the molten metal surface, and this time, it was performed 50 mm and 100 mm above the solidification starting point 8. 10 is a heat insulating material for the bath surface.

By using the casting method of the present invention described above, as shown in Table 1, conventional casting methods F, G (comparative example)
It is extremely superior in that it enables high-speed casting obviously, reduces the flaws on the surface of the slab, suppresses breakout, and does not require powder in the mold (lubrication by the melt of the surface protection material). I understand.

[Effects of the Invention] As described above, by using the under-solidification solidification casting method of the present invention, high-speed casting can be realized with solid lubrication, and casting accidents such as reduction of slab surface flaws and breakout can be suppressed.

In addition, since no powder in the mold is required, economical casting can be realized, and since the amount of fluctuation in the molten metal surface can be significantly tolerated, continuous casting operation can be facilitated and other excellent effects can be expected.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing an example of the casting method of the present invention. 1 ... Copper mold, 2 ... Cooling water flow path, 3 ... Ceramic piece, 4 ... Internal curvature surface, 5 ... Ceramics, 6 ... Immersion nozzle, 7 ... Molten metal, 8 ... Solidification starting point, 9 ……
Hot water surface, 10 ... Heat insulation material, 11 ... Insulation space

Claims (1)

[Claims] 1. In a continuous casting method using a mold made of copper or plated on the copper surface, which is lined with varying thickness of small piece ceramics on the entire inner wall, heat insulation of molten metal cast on the upper part of the mold Subsequently, the molten metal under-solidification casting method in continuous casting is characterized in that the molten metal is solidified under the molten metal surface through an inner curvature surface for cooling and solidifying the molten metal.