JPS626737A - Continuous casting mold for steel - Google Patents

Abstract

PURPOSE:To prevent the defect of a product and to improve the yield thereof by disposing a heat insulating layer to the specific part on the inside wall surface of a casting mold. CONSTITUTION:The heat insulating layer 3 is formed on the inside wall surface of the water cooled casting mold 1 by embedding magnesia-graphite, etc. therein. The heat insulating layer 3 is formed by covering the part from the top surface of a powder layer 9 to a meniscus part 8. A molten steel 6 is supplied from a tundish 4 via an immersion nozzle 5 into the casting mold 1 and powder is introduced from a powder supply device thereto form the powder layer 9. The heat insulating layer 3 prevents the dissipation of the heat from the powder layer 9 to the inside wall of the casting mold to suppress the temp. drop of the powder layer 9. The generation of slag bear is thus prevented and therefore the generation of the defect such as surface crack of the powder layer 9 is decreased. Since the segregation on solidification is decreased, the yield of the product is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a mold for continuous casting of steel, particularly a mold for powder casting.

(Conventional technology) Generally, continuous steel casting uses water-cooled copper molds.

Powder is added and the mold is vibrated in order to aid in the lubrication between the mold and the slab. Part of the powder covering the surface of the molten steel melts due to the sensible heat of the molten steel, and is separated into a powder layer and a molten layer.

As a prior art technology that provided a heat insulating layer on a part of the inner wall surface of the mold,
There is European Patent No. 83757. FIG. 4 shows an embodiment of this prior art, in which a heat insulating layer 13 is provided inside the inner wall 12 of the water-cooled mold 11 at a position corresponding to the meniscus 8. With this mold +1, the development speed of the solidified shell 7 can be suppressed, and hot cracking and segregation of the slab can be reduced.

(Problems to be Solved by the Invention) However, in the mold of the prior art described in L, the following problem occurs due to the addition of powder.

That is, since the inner wall of the mold is cooled and has high thermal conductivity, the temperature of the powder in contact with the inner wall surface decreases and becomes a lumpy solid layer (slag bear). This slag bear is then pushed into the solidified shell by the vibration of the mold, creating periodic irregularities (oscillation marks) on the surface of the slab. This oscillation mark is often caused by the sagging of the rolling coil.
It causes surface defects such as surface cracks. Therefore, the surface of the slab needs to be cleaned, and the product yield is reduced due to the occurrence of defective products.

(Means for Solving the Problems) The mold for continuous casting of steel according to the present invention is provided with a heat insulating layer on at least a portion of the inner wall surface of the mold that is in contact with the powder layer.

In reality, the heat insulating layer is provided over a range from slightly above the powder layer to slightly below the meniscus, taking into consideration the margin of space.

The heat insulating material forming the heat insulating layer requires the following properties to prevent oscillation marks and surface defects on the slab.

b) The heat flux flowing from the powder layer surface to the heat insulation layer is 50ca
Thermal conductivity shall be less than l/c+a2s. For this purpose, the following conditions must be met.

k/d≦0,05 where k (cal/cm”c 5ee) is the thermal conductivity of the heat insulating material, and d (c+s) is the thickness of the heat insulating layer.

Mouth) Must have excellent thermal shock resistance to prevent cracking of the insulation layer due to thermal shock.

c) The insulation material should not react with the molten powder and deteriorate.

Examples of materials having such properties include magnesia graphite, magnesia chromite, alumina, silicon nitride, and poron nitride.

The thickness of the section fj+ layer is preferably 1 mm or more. Further, in normal operation, the vertical width from directly below the powder layer to directly below the meniscus is about 30fffffi, and a heat insulating layer is provided in this range.

A heat insulating layer is formed by embedding a heat insulating material in the inner wall of the PI5 or spraying the heat insulating material on the surface of the inner wall of the mold.

(Function) The heat insulating layer prevents the dissipation of heat from the powder layer to the inner wall of the mold and suppresses the temperature drop in the powder layer. As a result.

The generation of slag bears is prevented by IF, and slag bears are not pushed into the solidified shell by the vibration of the mold.

(Example 1) FIG. 1 shows a mold of the present invention, in which magnesia-graphite is embedded in the surface of an inner wall 2 of a water-cooled copper mold 1 to form a heat insulating layer 3. The thickness of the heat insulating layer 3 is 2cm.

Further, the heat insulating layer 3 covers from the upper surface of the powder layer 9 to the lower end of the powder fused layer 10, that is, the position of the meniscus 8, and its lower width 9E is 50 ram.

Using the above mold, Al-9i guild steel for cold-rolled thin plates was cast. Molten steel 6 is supplied to the mold 1 from a tundish 4 through an immersion nozzle 5, and powder is introduced from a supply device (not shown).

No slag bears were generated during casting. The slab thus obtained was then rolled into a thin plate to form a coil.

FIG. 2 shows the surface flaw occurrence rate of the above-mentioned coil in comparison with that of the conventional coil. As is clear from FIG. 2, the surface flaw occurrence rate of the rolled coil is about 1/3 that of the conventional one.

(Example 2) Silicon nitride was thermally sprayed onto the inner wall surface of a water-cooled copper mold using a plasma arc to form a heat insulating layer. The dimensions of the insulation layer are the first
This is the same as the embodiment.

Using the above mold, Al-9i killed steel for cold-rolled thin plates was cast. No slag bears were generated during casting. The slab thus obtained was then rolled into a thin plate to form a coil.

! Figure 2 shows the end of the coffin of Ei-men, 91-11/, and the end of the coffin. Similar to the first embodiment, the surface flaw occurrence rate of the rolled coil is about 1/3 that of the conventional one.

This invention is not limited to the above embodiments. For example, as shown in FIG. 3, the thickness of the heat insulating layer 3 near the meniscus 8 may be gradually thinned downward. As a result, the temperature of the lower part of the heat insulating layer 3 decreases, and the solidification of the molten steel 6 near the meniscus 8 is promoted without causing the slag bears to be pushed in.

(Effects of the Invention) By using the mold of the present invention, oscillation marks are reduced, and defects such as curling and surface cracks in rolled coils are reduced. Furthermore, since the cooling rate of the solidified shell is reduced, diffusion in the solid phase is promoted and solidification segregation is reduced.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the present invention, which is a longitudinal cross-sectional view of a mold during casting of a slab, and Fig. 2 shows coils obtained by rolling slabs cast using molds of the present invention and a conventional mold. FIG. 2 is a diagram showing the surface scratch incidence rate of FIG. 3 is a cross-sectional view of another embodiment of the heat insulating layer, and FIG. 4 is a vertical cross-sectional view of a conventional n-type during slab casting. Engineering, 11... Mold, 2.12... Mold inner wall, 3...
- Heat insulation layer, 6... Molten steel, 7... Solidified shell, 8... Meniscus, 9... Powder layer, 10... Powder molten layer.

Claims (1)

[Claims] A mold for continuous casting of steel, characterized in that a heat insulating layer is provided on at least a portion of the inner wall surface of the mold that is in contact with a powder layer.