JPH0847748A - Mold for continuous casting - Google Patents

Abstract

PURPOSE:To stably provide slab with excellent surface by forming the sprayed coating made of hard metal, cermet or ceramics which is sealing treated with the refractory material on the molten metal. CONSTITUTION:Because pores and cracks present on the surface of the sprayed layer are covered with the sealing agent, the atmospheric gas is prevented from being thermally expanded and inflated out of the surface of a mold even when the sprayed layer is brought into contact with the molten metal and reaches the high temperature, and the solidification delay of the molten metal is not generated in the part where pores or cracks are present, and the slab with excellent surface condition is obtained. In addition, even if the sealing is executed on the sprayed layer, only a part of pores or cracks on the surface are covered by the sealing material, and the reduction of the heat reduction speed of the mold and the improvement of the wear resistance which are the original purpose of the sprayed layer are not damaged. The slab with excellent surface condition is obtained while the defects such as cracks, recesses or porosities of the slab are prevented by uniformly forming the solidified shell through the reduced heat removal speed of the mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting mold for continuously casting and solidifying molten metal to produce a slab.

[0002]

2. Description of the Related Art Currently, molten metal (hereinafter referred to as "molten metal")
For example, the following method is well known as a continuous casting method for continuously casting and solidifying (. (A) A general method using an open-ended mold. (B) Strip casting method for continuously producing thin slabs with a thickness of several mm using a rotating cooling roll as a mold, a) single roll method shown in FIG. 1, b) twin roll method shown in FIG. Top-pouring method, c) Side-pouring method with different diameter twin rolls as shown in Fig. 3. (C) Using a pair of rotating thin steel plate endless belts with cooled back surface as a mold, or using an endless belt-shaped mold composed of a pair of rotationally moving cooling blocks, several tens of mm
Endless belt method for continuously producing thin cast pieces, a) inclined twin belt method shown in Fig. 4, b) double block casting method shown in Fig. 5.

By the way, in such a continuous casting method, it has been proposed to use a mold having a sprayed coating formed on the surface in contact with the molten metal, mainly in the following two reasons, and in the actual operation as well. The use of molds with different thermal spray coatings has become popular. B) Slow cooling of the solidified shell Reduce the heat removal rate of the mold so that the slab (solidified shell) is slowly cooled. As a result, the solidified shell is less likely to be thermally deformed, and the solidified shell having a uniform thickness is formed.
Then, defects such as cracks on the surface of the slab are greatly reduced, and a slab of good quality can be obtained. (2) Prolonging the life of the mold Generally, the copper alloy used as the mold material has a low hardness, so it is plated with a metal (Ni, Cr, etc.) that has excellent heat resistance, but it is worn or damaged and the slab It adversely affects the surface quality and cannot withstand long-term operation. Therefore, by spraying a material having high hardness and excellent heat resistance to coat the surface of the mold, the useful life of the mold is extended.

The following can be exemplified as proposals relating to a mold having a sprayed coating. For example,
Regarding the general continuous casting method (hereinafter referred to as “conventional continuous casting method”) in which the upper and lower open molds are vibrated (oscillated), (a) the heat removal rate of the mold is suppressed to obtain a uniform thickness. A water-cooled copper mold (Japanese Patent Laid-Open No. 55-156643) in which "powder of Ni or Cr mixed with ceramics" is sprayed on the inner surface in order to form a solidified shell and obtain a slab without cracks, (b) Heat resistance To improve wear resistance and high temperature wear resistance,
Water-cooled copper mold sprayed with mixed powder of Ni-Cr alloy and Cr carbide on the surface (JP-A-58-81544), (c) High temperature hardness and thermal expansion on the surface to improve wear resistance There has been proposed a water-cooled copper mold (Japanese Patent Laid-Open No. 61-289948) in which a metal having a rate substantially equal to that of the base material is joined by diffusion welding or explosion welding and then hard metal, cermet or ceramics is sprayed.

Further, in the strip casting method using a rotating cooling roll as a mold, (a) Ni base plating is applied to the surface of a roll base material in order to improve high temperature wear resistance and extend roll life. After that, a cooling roll mold in which a high hardness ceramic substrate is sprayed by the explosive spraying method (JP-A-59-163056), (b) slow cooling to form a uniform solidified shell and prevent internal defects Therefore, a cooling roll mold (Japanese Patent Publication No. 5-23853) having a surface coated with a sprayed metal oxide or nitride has been proposed.

Further, in the endless belt type thin slab continuous casting method, in order to reduce the heat load on the belt due to the molten metal to prevent the belt from being deformed or damaged, and to reduce the slab defects such as cracks, A belt-shaped mold (JP-A-59-174254) having a surface coated with a refractory ceramic has been proposed.

As described above, in any of the continuous casting methods, when a sprayed coating of hard metal, cermet or ceramics is provided on the surface of the mold, the quality of the cast product is improved by reducing the heat removal rate of the mold. It has become a well-known matter now that the effect and the effect of extending the life of the mold based on the improvement of the wear resistance of the mold can be obtained. However, on the other hand, when a sprayed coating of hard metal, cermet or ceramics is provided on each of the above-mentioned molds, the surface of the obtained slab has a small crater-like recess with a diameter of about several mm (hereinafter referred to as "crater-like defect"). ) Occurred on the entire surface, and the surface skin was not always improved.

As mentioned above, this is a conventional continuous casting process,
This is a problem pointed out in either the strip casting method or the endless belt type thin slab continuous casting method, and the same crater-like defects tend to occur on the surface skin of the slab obtained by the mold having the sprayed layer. There was,
In particular, when an ultra-thin cast piece with a thickness of about 1 mm or less is produced by the strip casting method in which the obtained cast piece has a small thickness, a hole with a diameter of about several mm (a portion where the cast piece is not formed) is formed in the cast piece. In some cases, a satisfactory thin plate could not be obtained.

Therefore, attempts have been made to change the method of thermal spraying (plasma type, explosive type, etc.) and to polish and flatten the surface of the sprayed coating after the construction. The tendency for crater-like defects to occur on the surface remained unchanged. For this reason, if rolled as it is, crater-like defects will remain in the product as flaws and patterns. Therefore, after casting, select a crater-like defect that is not severe (not enough to open holes) and cut the surface of the slab. However, it was necessary to carry out rolling after removing defects.

In view of the above, an object of the present invention is to provide a continuous casting means capable of stably obtaining a slab having a good surface texture by using a mold provided with a thermal spray coating.

[0011]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have stated that "there are crater-like defects and holes in the slab when continuous casting is performed using a mold having a sprayed coating. It was necessary to investigate the cause, "and conducted the following studies and investigations in the process. That is, after spraying various materials on the surface of a block of the same material as the continuous casting mold to prepare a sample of "mold having a sprayed coating", this is used in molten metal under the same conditions as the actual operation and temperature and components. It was dipped in the solution for several seconds to form a solidified shell on its surface, and the surface skin and solidified structure of the obtained shell were investigated.

Then, when the above investigation results were examined in detail, the cause of "the crater-like defects on the surface of the slab" which tends to occur in continuous casting using a "mold having a sprayed coating" is the sprayed layer (coating). The presence of atmospheric gas (usually air) in the open pores and cracks on the surface of the.

That is, as shown in FIG. 6, although there are some differences depending on the thermal spraying method and the thermal spraying material, many pores generally exist from the surface to the inside of the thermal spraying layer. Therefore, the molten metal is poured into a mold having such a sprayed layer,
When the surface of the thermal spray layer contacts the molten metal and reaches a high temperature, the atmospheric gas (air) existing in the pores (even the small pores where the molten metal does not enter) opening on the surface of the thermal spray layer expands due to thermal expansion. It bulges out of the surface, forming a partial gas insulation layer. Therefore, only that part becomes adiabatic and the solidification of the molten metal is delayed. As a result, in the initial stage of solidification with a solidification time of 1 second or less, a solidified shell is formed in the normal portion where the expanded gas is not present, but a solidified shell is not formed in the portion where the gas is present. In the slab, there is a hole in which no shell is formed. Then, as the solidification progresses, a shell is formed later in the portion where the gas is present,
It was found that a dent remained on the surface, and this became a crater-like defect. This phenomenon also occurs when microcracks are present on the surface of the sprayed layer.

Therefore, further research was conducted in search of an effective means for suppressing the above-mentioned phenomenon without any inconvenience, and it was found that "a sprayed film formed on the surface of a mold is sealed with a refractory material to form a sprayed film. If the pores and crack openings exposed on the surface are blocked with a refractory material, the atmosphere gas inside the pores and cracks will not swell to the mold wall surface even if it comes into contact with the molten metal during casting. It is possible to obtain new knowledge that "crater-like defects are not generated on the surface of the formed slab."

The present invention has been completed based on the above-mentioned findings and the like. "A cooling mold for continuous casting for solidifying a molten metal to continuously produce a slab, It has a thermal sprayed coating of hard metal, cermet or ceramics sealed with a refractory material. "
It has a great feature.

As described above, the present invention provides at least a continuous casting cooling mold for continuously producing cast pieces by solidifying a molten metal of ferrous metal such as iron, carbon steel, alloy steel or the like and other non-ferrous metals. On the contact surface with the molten metal, a coating of hard metal, cermet or ceramics is formed by thermal spraying, and further pores and cracks present on the surface of the thermal sprayed layer are sealed with a refractory substance such as high melting point oxide, This is a mold for continuous casting that forms a sprayed coating that does not cause crater-like defects on the surface of the slab, but the "continuous casting cooling mold" that is the subject here is the "opening of both ends that is usually used in conventional continuous casting processes". Mold (immersion nozzle type, direct connection type of tundish and mold used for horizontal continuous casting, eg
"Materials and processes" such as continuous casting of composite billets as described in Vo15 (1992), page 1330) "," Cooling rolls used in strip casting continuous casting "and" endless belts " It includes any of an endless belt and a cooling block "used in the continuous casting method.

Further, the sprayed coating formed on at least the surface of the mold that comes into contact with the molten metal is "slow cooling of the solidified shell" or "long life of the mold" as conventionally known.
It is for the hard metal such as Ni-Cr alloy as the thermal spraying material for forming the sprayed coating, cermet such as _{WC-Co, ZrO 2, Al} 2 O 3, SiO 2, BN, Si 3 N ₄ ,
Either ceramics such as SiC or a mixture thereof is used. For forming the sprayed coating, any spraying method such as plasma type, explosion type, arc type and the like may be used. In this case, Ni or Ni alloy or the like may be plated on the surface of the mold base material as an underlayer (intermediate layer), and thermal spraying may be performed thereon to form the thermal sprayed layer.

In the present invention, the material (sealing material) for sealing the pores and cracks on the surface of the sprayed coating is a refractory material such as zirconia, alumina or silica. (Zirconia, alumina,
A sol based on an oxide such as silica), a boric acid aqueous solution, water glass or an alkyl silicate is used as a treating agent (sealing agent). Then, these are sufficiently impregnated into pores and cracks on the surface of the sprayed coating, and then heating and curing and removal of the gasification substance are performed, and the openings of pores and cracks present on the surface of the sprayed coating are zirconia,
It is plugged with a refractory oxide such as alumina, silica or boron oxide, or other refractory material, and the sealing treatment is completed.

Thus, as the sealing agent used in the sealing treatment, sol based on oxides such as zirconia, alumina or silica, aqueous solution of boric acid, water glass or alkyl silicate are preferred examples. However, these drugs will be described.

The above-mentioned "sol" means zirconia (Zr
O ₂ ), alumina (Al ₂ O ₃ ) or silica (SiO ₂ ) colloidal particles are dispersed in a liquid such as water or alcohol, and the colloidal particles are very small (0.005 to 0.3).
.mu.m), so that it can penetrate into pores and cracks having a size of several .mu.m on the sprayed surface together with the liquid. After impregnation, if only the liquid is heated to vaporize and evaporate, the agglomerates of colloidal particles remain in the pores and cracks, and ZrO
Oxides such as ₂ , Al ₂ O _{3 and} SiO ₂ block pores and cracks.

When the "boric acid aqueous solution" is heated after being impregnated in the pores and cracks, water as a solvent is first evaporated to leave a solid boric acid (H ₃ BO ₃ ) substance. Then, when the temperature is further raised (about 300 ° C.), boric acid changes to boron oxide (B ₂ O ₃ ), and at temperatures of 300 ° C. or higher, it stably exists even in pores and cracks on the surface of the sprayed layer. Block pores and cracks.

"Water glass" is a solution of an alkali silicate salt obtained by melting silicon dioxide and alkali in water, and sodium silicate using Na ₂ O as an alkali is known as a typical example. This is because when impregnated into pores or cracks and then heated to remove water, refractory glassy Na ₂ O.nSiO ₂ remains to close the pores or cracks.

"Alkyl silicate" has the chemical formula "Si
A tetraalkoxysilane represented by the formula (OR ¹ ) ₄ "is a co-hydrolysis condensate of a tetraalkoxysilane represented by the formula" R ² Si (OR ³ ) ₃ "or a formula" Si (O
It is a mixture of a hydrolyzed condensate of tetraalkoxysilane represented by R ¹ ) ₄ ”and a hydrolyzed condensate of trialkoxysilane represented by the chemical formula“ R ² Si (OR ³ ) ₃ ”. In the above chemical formula, R ¹ , R ² and R ³ are as follows. R ¹ : an alkyl group having 1 to 4 carbon atoms, R ² : a hydrocarbon group having 1 to 6 carbon atoms, R ³ : an alkyl group having 1 to 4 carbon atoms. When the pores and cracks on the surface of the sprayed layer are impregnated with this alkyl silicate and heated, water and alcohol generated by hydrolysis are removed, a siloxane network is formed and gelled, and a dense sealing treatment with siloxane is performed. You can

Of course, the pore-sealing agent is not limited to the above-mentioned ones. Even if chemicals other than these are used, a substance such as an oxide having fire resistance after impregnation and heat curing may cause pores and cracks. Any material can be used as long as it prevents the gas remaining in the pores and cracks from bulging from the surface of the thermal spray coating when sealed and then heated.

Since these pore-sealing agents need to be sufficiently impregnated into fine pores and cracks on the surface of the sprayed layer, a solvent such as water or alcohol may be added as necessary to adjust the viscosity and surface tension. It is effective to do. As means for impregnating the pores and cracks on the surface of the sprayed layer with a pore-sealing agent, brush coating, spray coating, dipping or the like can be applied. In this case, the mold with the spray coating formed in advance is placed under vacuum to degas the gas of pores and cracks of the spray coating, and then brush coating, spray coating, dipping, etc. are carried out for more effective impregnation. Can be made.

After impregnating the pore-sealing agent, it is necessary to remove the solvent of the pore-sealing agent remaining in the pores and cracks. Therefore, the mold impregnated with the pore-sealing agent is naturally dried and then heated to evaporate a solvent such as water or alcohol. At this time, it is desirable to raise the temperature relatively slowly in order to avoid rapid reaction and evaporation. The heating temperature varies depending on the type of the sealing agent and its solvent, but is preferably at least the mold surface temperature (300 ° C. or higher) during the casting operation, and is maintained at that temperature for 30 minutes to several hours.

As a specific method of determining the heating temperature, there is a method of measuring the weight loss of the sealing agent by thermal analysis. That is, it is a method of increasing the temperature to obtain the temperature when the weight reduction amount is almost eliminated. By heating above this temperature and holding for a certain period of time, the gasifying substances in the sealing agent are completely eliminated, and there is no adverse effect during the casting operation. However, if the heating temperature is too high, the base material of the mold (mainly copper alloy) is thermally deformed, so it is desirable to set the heating temperature to 500 ° C. or lower. However, even if impregnation with a sealing agent and heat treatment are performed, if the heat treatment temperature is not sufficient, the solvent remaining in the pores and cracks may vaporize and expand during the casting operation and swell from the thermal spray coating. , It is necessary to pay attention to the heating temperature. If possible, refractory substances (ZrO ₂ , Al ₂ O ₃ , SiO ₂ etc.) in the pores and cracks after impregnation with the sealing agent and heat treatment.
It is preferable to heat so that only these remain and these will fill the pores and cracks on the surface of the sprayed layer. In order to complete the sealing, it is sometimes preferable to repeat the above-mentioned steps from the impregnation of the sealing agent to the heat treatment (sealing treatment) twice or more.

[0028]

In the continuous casting mold according to the present invention, as shown in FIG.
As shown in, since the pores and cracks existing on the surface of the sprayed layer (sprayed coating) are blocked by the sealing material (refractory material), even when the sprayed layer comes into contact with the molten metal and has a high temperature, Atmosphere gas (air) does not thermally expand from the pores or cracks and swell to the surface of the mold (sprayed layer), so that there is no delay in the solidification of the molten metal at the presence of pores or cracks, and the surface texture A good slab can be obtained.

Further, even if the thermal sprayed layer is subjected to sealing treatment, only a small part of the pores and cracks on the surface are closed with the sealing material, so that the heat removal rate of the mold, which is the original purpose of the thermal sprayed layer, is required. And does not impair the improvement of wear resistance. Therefore, according to the present invention, it is possible to obtain a slab with good surface properties while preventing defects such as cracks, dents or porosity of the slab by uniformly forming a solidified shell by reducing the heat removal rate of the mold. Further, by improving the wear resistance of the mold, the life of the mold can be extended and the effects such as obtaining a slab having good surface properties can be secured.

By the way, generally, for the purpose of improving the corrosion resistance of a material coated with a porous thermal spray coating, the pores of the thermal spray coating are blocked with a sealing material mainly composed of vinyl resin, phenol resin, polyurethane resin or the like. Although the sealing treatment was known, in the case of the mold used for continuous casting, the temperature is high because it comes into contact with the molten metal, although it may vary somewhat depending on the operating conditions, mold material, sprayed layer thickness, etc. Thirty
Needless to say, the above sealing treatment using a resin as a sealing material cannot be applied because the sealing material burns or evaporates during casting operation. Furthermore, the crater-like defects that tend to occur on the surface of the slab obtained by the continuous casting mold having the sprayed coating, are caused by the swelling of the atmospheric gas present in the micropores or cracks of the sprayed coating surface portion. Based on the above, there has been no report so far that this can be effectively prevented by sealing the thermal spray coating with a refractory material.

Next, the present invention will be described more specifically by way of examples.

【Example】

Example 1 An upper and lower open mold having a sprayed coating for sealing treatment on the inner wall surface was prepared as shown below. Mold base material: The material is copper alloy and the wall thickness is 20 mm, mold size: width 1000 mm x length 900 mm x thickness 100 mm, thermal spraying purpose: improved wear resistance and mold life, thermal spraying condition: a) Ni plating of 50 μm thickness as a base (intermediate layer) on top, and b) Ni-Cr alloy sprayed layer of 100 μm thickness by gas spraying method as a base on Ni plating, c) Ni-Cr sprayed layer WC-10% C by plasma spraying method
o Apply a sprayed layer to a thickness of 150 μm. Sealing treatment: Sealing agent: Alumina hydrate (colloidal Al ₂ O ₃ particles, average particle size 0.02 μm), Impregnation method: Brush coating, heat treatment: 1 day natural drying, 2 ° C / min Temperature rises to 100 ° C
Hold for 1 hour, then raise the temperature further and hold at 350 ° C for 1 hour, then air cool.

Next, a continuous casting test of low carbon aluminum killed steel was conducted using the above mold. The operating conditions at this time were as follows. Molten metal amount: 50ton, Casting speed: 3.0m / min, Mold vibration condition: Cycle ... 240cpm, Stroke ... 8
mm.

Further, as a comparative test, a continuous casting test under the same conditions was carried out using a thermal spraying mold which had not been subjected to a sealing treatment. As a result, in the case of using the thermal spray mold with the sealing treatment according to the present invention, the obtained cast piece (width 1000 mm × thickness
The surface texture of 100 mm) was good only because the oscillation marks due to the vibration of the mold were seen, and therefore a good product was obtained by hot rolling this slab. Also, the mold is 250
It has been confirmed that there is no problem even if casting is performed more than once, and even if the sealing treatment is performed, improvement of wear resistance, which is the original purpose of thermal spraying, can be achieved.

On the other hand, in the case of a comparative test using a mold which was not sealed, a large number of small crater-like pits (diameters having a diameter of 1 to 3 mm) other than the oscillation marks were formed on the slab. In particular, a large number of dents (grooves having a diameter of 5 to 10 mm) were frequently found up to about 10 m at the beginning of casting. For this reason, the surface of the slab must be entirely cut before hot rolling so that no flaws remain on the product.

[Example 2] A mold (cooling roll) of the twin roll top pouring system (system shown in Fig. 2) having a sprayed coating for sealing treatment on the surface thereof was prepared as shown below. Mold base material: Copper alloy material with a wall thickness of 20 mm, Mold size: Body length 400 mm x Diameter 600 mmφ, Thermal spraying purpose: Reduction of heat removal rate (slow cooling), Thermal spraying condition: a) Base material on the base metal (intermediate) Layer) as 50 μm thick with Ni plating, and (b) Ni plating as a base with a gas spraying method as a Ni-Cr alloy sprayed layer with a thickness of 50 μm, and c) plasma spraying method on the Ni-Cr sprayed layer At “ZrO ₂ −
8% Y ₂ O ₃ sprayed layer ”is applied to a thickness of 200 μm. Sealing treatment: Sealing agent: Alkyl silicate {Chemical formula" Si (O
R ¹⁾ ₄ "tetraalkoxysilane chemical formula shown by the" co-hydrolytic condensate of a trialkoxysilane represented by R ² Si (OR ^{₃₎ 3} 'or formula, "Si (OR ¹⁾ _4'
A mixture of a hydrolyzed condensate of tetraalkoxysilane represented by and a hydrolyzed condensate of a trialkoxysilane represented by the chemical formula “R ² Si (OR ³ ) ₃ ”, impregnation method: coating by spraying, heat treatment ... 1 day After natural drying, heat up at 1 ℃ / min and 450 ℃
Hold for 1 hour and air cool. The heating temperature is 1 in advance.
The sealing agent heat-treated at 20 ° C. was subjected to thermal analysis, and the weight change was determined. The results of this thermal analysis are shown in FIG. 8. As is clear from the results shown in FIG.
Since the weight change is large, the heating temperature was set to 450 ° C.

Next, a continuous casting test of SUS304 stainless steel was conducted using the above mold (cooling roll). The operating conditions at this time were as follows. Amount of molten metal: 2ton, Casting speed: 50m / min,

As a comparative test, a continuous casting test under the same conditions was also carried out using a thermal spraying mold (thermal spraying roll) which had not been subjected to sealing treatment. As a result, when the sealing-processed thermal spraying mold (spraying roll) according to the present invention is used,
The surface properties of the obtained slab (width 400 mm x thickness 2.1 mm) were good, and no flaws such as dents and cracks were observed.

On the other hand, in the case of the comparative test using the thermal spraying mold (thermal spraying roll) which was not subjected to the sealing treatment, although no cracks and cracks were found on the surface of the slab, small crater-like recesses (having a diameter of A large number of defects (1 to 3 mm) were generated, and in particular, there was also a part (hole) where the solidified shell was not formed up to about 10 m at the beginning of casting. For this reason, the slab could not be used because flaws remain in the product even after rolling.

[Example 3] A mold (belt) of the inclined twin-belt system (system shown in Fig. 4) having a sealing sprayed coating on the surface thereof was prepared as shown below. Mold base material: Low carbon aluminum killed steel with a wall thickness of 1.5 mm
, Mold size: Width 1000mm x Length 2.9m x Thickness 50mm, Thermal spraying purpose: Reduction of heat removal rate (slow cooling), Thermal spraying condition: a) Ni-Cr by gas thermal spraying method as base on base material The alloy sprayed layer is applied to a thickness of 50 μm, and b) The Al ₂ O ₃ sprayed layer is applied to a thickness of 150 μm on the Ni—Cr sprayed layer by the explosive spraying method. Sealing treatment: Sealing agent ... Boric acid, Impregnation method ... Spray coating, Heat treatment ... 1 day natural drying, and then heating at 2 ° C / min to 400 ° C
Hold for 1 hour and air cool. The heating temperature is 1 in advance.
The sealing agent heat-treated at 20 ° C. was subjected to thermal analysis, and the weight change was determined. The results of this thermal analysis are shown in FIG. 9. As is clear from the results shown in FIG.
Since the weight change was large at 400 ° C. and became constant at 400 ° C., the heating temperature was 400 ° C.

Next, a continuous casting test of low carbon aluminum killed steel was conducted by a slant type twin belt type thin slab continuous casting machine using the above mold (belt). The operating conditions at this time were as follows. Amount of molten metal: 50ton, Casting speed: 4.0m / min,

As a comparative test, a continuous casting test under the same conditions was also carried out using a thermal spraying mold (belt) which had not been subjected to sealing treatment. As a result, in the case of using the thermal spraying mold with a sealing treatment according to the present invention (spraying belt), the surface properties of the obtained slab (width 600 mm × thickness 50 mm) are good, and flaws such as dents and cracks are observed. I couldn't see it.

On the other hand, in the case of the comparative test with the thermal spray mold (thermal spray belt) which was not sealed, no cracks were found on the surface of the slab but small crater-like dents (diameter was Many defects of 1 to 3 mm occurred. For this reason, the surface of the slab must be entirely cut before hot rolling so that no flaws remain on the product.

[0043]

[Summary of Effects] As described above, according to the present invention, the crater-like defects can be formed without impairing the reduction of the heat removal rate and the improvement of the wear resistance, which are the original purpose of the mold having the sprayed coating. It is possible to provide a mold for continuous casting with a sprayed coating that can be stably prevented, and it becomes possible to manufacture a continuous cast slab that is sound and has good surface quality with a long mold life, which is industrially useful. The effect is brought about.

[Brief description of drawings]

FIG. 1 is an explanatory diagram relating to a single roll type strip casting method.

FIG. 2 is an explanatory view of a twin-roll top pouring type strip casting method.

FIG. 3 is an explanatory diagram related to a strip casting method of a different diameter twin roll side pouring method.

FIG. 4 is an explanatory diagram related to an endless belt type thin slab continuous casting method of a tilt type twin belt method.

FIG. 5 is an explanatory diagram related to the endless belt type thin slab continuous casting method of the bi-block mold method.

FIG. 6 is an explanatory diagram related to a slab generation state when a mold for continuous coating with a thermal spray coating that has not been subjected to a sealing treatment is used.

FIG. 7 is an explanatory diagram related to a slab generation state when a mold for continuous coating with a sprayed coating having a sealing treatment is used.

FIG. 8 is a graph showing the results of investigating the weight change of a sealing agent (alkyl silicate) by thermal analysis.

FIG. 9 is a graph showing the results of investigation of the weight change of the sealing agent (boric acid) by thermal analysis.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C23C 4/18

Claims (1)

[Claims] 1. A cooling mold for solidifying a molten metal to continuously produce a slab, which comprises a hard metal, cermet or ceramics whose contact surface with the molten metal is sealed with a refractory material. A casting mold for continuous casting, comprising a thermal spray coating.