JPH06134553A - Mold for continuously casting thin cast slab and method for working surface thereof - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a mold that does not cause cracks and gloss on the surface of a slab in a synchronous continuous casting process, and a processing method thereof. [Structure] A large-diameter depression A ₁ required as a starting point for solidification nuclei by a shot blasting method on the surface of a synchronous continuous casting mold.
In addition, it consists of a mold in which the small-diameter depressions A ₂ necessary for the gentle cooling effect are properly distributed, and two types of steel balls having different steel diameters for shot blasting are mixed and projected onto the mold surface to produce the mold surface. To process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving mold casting apparatus, for example, a twin-drum system using a pair of cooling drums having a water cooling mechanism inside, a single-drum system using one cooling drum, or a cooling drum. The present invention relates to a surface shape of a mold and a surface processing method for the mold in a thin cast piece casting apparatus such as a drum-belt system in which a molten metal pool is formed between the belt and the belt.

[0002]

2. Description of the Related Art In a synchronous continuous casting method, for example, a molten metal (molten metal) in a molten metal pool composed of a cooling drum and side dams is cooled and solidified by a cooling drum to form a solidified shell,
This is a method for directly producing a thin cast piece having a wall thickness of about 1 to 10 mm, which is close to the final shape. Therefore, it is extremely important to produce a thin cast article having a good surface property.

In such casting, it is an important subject to maintain the surface quality of the slab at a high level in a stable manner. Therefore, as a means for achieving uniform formation of a solidified shell,
For example, Japanese Patent Application Laid-Open No. 60-18449 discloses a technique in which a large number of depressions are provided on the peripheral surface of the cooling drum so as to form an air gap serving as a heat insulating layer between the cooling drum and the solidified shell.

Further, as a modification of such a technique, Japanese Patent Laid-Open No. 64-83342 discloses a technique in which the depth, the diameter, the distance between the depressions, the motif of the depressions, etc. are specified. . Furthermore, as a processing means of the depression,
Means such as shot blasting electrolytic method, electric discharge machining method and electron beam machining method are disclosed in JP-A-62-254953.

[0005]

In order to continuously obtain a preferable thin cast piece by using a moving mold type continuous casting machine, when a recess is formed on the outer peripheral surface of a mold, for example, a cooling drum, by a shot blast method in particular. The size and distribution of the depressions are extremely important. On the outer peripheral surface of the cooling drum which is in contact with the molten metal, solidification starts from the recesses formed in the drum, but if the diameter of the recess is too small, it cannot be the solidification start point. As a result, uneven solidification occurs, causing cracks and uneven surface solidification due to wrinkles.

In order to increase the solidification starting point and promote uniformity, the diameter of the steel ball is further increased and engraved on the drum surface.
Large undulations occur at a constant pitch in the drum width direction, and when molten metal is cast on the drum surface, large molten metal wrinkles occur on the surface of the slab. Also, if there is a continuous flat portion on the outer peripheral surface of the cooling drum, cracks may occur at the boundary between the flat portion and the hollow portion,
It remains as uneven coagulation. Therefore, it is necessary to make the size and distribution of the steel balls proper without increasing the recess diameter more than necessary, but in the prior art, there is no clear suggestion regarding the size distribution of the steel balls during engraving. Absent.

The present invention solves the problems of the prior art in the case of processing the distribution of the depressions of the cooling mold by the shot blasting method in the continuous casting of thin cast slabs, which results in cracks and uneven gloss on the surface. It makes it possible to produce a cast piece free from slabs.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides that the surface of a moving mold of a synchronous continuous casting apparatus for thin cast pieces has a surface area of 90% or more of the peripheral area of the moving mold. Of 50 to 200 cavities having a circular or oval opening having a diameter of 0.4 to 1.0 mm and engraved by a shot blasting method over 1 cm ² , and cavities having a diameter of 0.3 mm or less, and The remaining surface is characterized by a flat part having a surface roughness of 10 μm or less, and two types of steel balls having different diameters are mixed on the moving transfer surface of a continuous casting machine to perform shot blasting. It is characterized in that the mold surface is processed.

The present invention will be described in more detail below. The present invention forms a cooling mold surface as described above by mixing and shot two types of steel balls on the surface of a mold for continuous casting of thin cast slabs, which makes it extremely easy and sound. A slab can be obtained. In the present invention, the initial depression is a depression formed on the surface of a smooth cooling mold in which the depression is not formed. The initial depressions are 0.4 to 1.0 mm and 50 to 200 depressions / cm.
^{In addition to} being distributed in the range of ² , the dents of 0.3 mm or less are distributed almost all over the remaining surface.

In order to become the solidification starting point, the large depression must be 0.4 mm or more. In addition, a small-diameter recess reduces cooling unevenness with a large recess on the mold surface, so 0.3 mm or less is effective. Further, the flat portion of the mold surface is preferably as small as possible in order to prevent unevenness of the surface structure, and is preferably at least 10% or less.

The area ratio of the flat portion in the present invention is defined by the following equation (1). Where S is the peripheral area of the cooling drum, and Si is the flat area of the cooling drum.

The flat portion is a portion having a surface roughness of 10 μm or less. At this time, the area ratio of the flat portion can be measured by simply performing image processing on the surface of the drum surface. That is, carbon spray is applied to the surface of the drum, and a rake book is taken by the fish hunting method to quantify the area ratio of the blackened portion. In the present invention, it is subjected to the shot blasting, when forming a desired recess in the cooling mold, the shot blast D ₁ of the order to form a large diameter d ₁ than 0.4 mm 0.
The shot blast D ₂ for forming the depression d _{2 of} 3 mm or less is mixed and processed. By subjecting a cooling mold having a flat surface to shot blasting, two types of large and small depressions need to collide with each other almost randomly.

When processing is performed with the same shot diameter, the distribution of depressions is normally distributed within a certain range, so two types of distribution cannot be formed. Therefore, by making the shot diameter two kinds, the distribution of the depressions can be made two kinds, and the distribution according to the example of the present invention can be reproduced. In this case, since the large diameter D ₁ and the small diameter D ₂ are randomly stamped on the material on the drum surface, the number of the large diameter D ₁ shots and the small diameter D ₂ shots can be set within the range satisfying the expression (2). preferable.

3% ≦ D ₁ / (D ₁ + D ₂ ) ≦ 40% (2) Although this ratio varies depending on the material of the drum surface, for example, a Cu mold is plated with Ni of 0.5 to 2 mm. In this case, if this ratio is less than 3%, it becomes a solidification nucleus 0.4mm
The number of the above depressions is small, uneven solidification occurs, and cracks occur. On the other hand, when it is more than 40%, dents of 0.4 mm or more continue, or large vertical undulations occur,
The slab surface quality is deteriorated.

If the shot diameter is less than 0.15 mm, the kinetic energy of the shot is small and it is difficult to obtain an effective depression. Therefore, the shot diameters D ₁ and D ₂ are expressed by the equation (3),
It is preferable to satisfy the expression (4). 0.50 mm ≤ D ₁ ≤ 1.1 mm (3) 0.15 mm ≤ D ₂ ≤ 0.4 mm (4) When casting a slab with a cooling mold having a recess formed in an appropriate range in this way, It is possible to prevent surface fine cracks and uneven gloss at the same time.

Further, since these dents wear with the casting amount, it is necessary to rework them depending on the wear. In addition,
The depression processing is preferably performed in a nitrogen atmosphere. As a result, it is possible to prevent the roll surface temperature from rising during the processing to promote the oxidation.

[0017]

The present inventors have conducted various studies on the depressions of the cooling mold, the surface cracks of the slab and the unevenness of surface solidification, and found that it is necessary to form large-diameter depressions necessary as solidification nuclei in a certain range. It was Furthermore, the present inventors have found that the unevenness of gloss on the surface of the slab can be eliminated by forming depressions of small diameter in these large diameter gaps.

FIG. 3 shows the cross-sectional shape of the depression, in which a larger and deeper depression A ₁ (diameter d
₁ , the depth l ₁ ) is smaller and the shallow dimple A ₂ (diameter d ₂ , depth l ₂ ) is formed by the small shot dimples. The large depression A ₁ comes into contact with the molten steel surface,
Solidification nuclei are generated to promote uniform solidification, and the small pit A ₂ around the pit increases the gas gap between the drum and the solidification shell to gently cool the surface of the slab, and further to the pit A ₁ necessary for the solidification nuclei. It was confirmed that unevenness of solidification on the surface can be eliminated by reducing the difference in cold speed from the depression A ₂ of the above.

It was also confirmed that the depressions A ₁ and A ₂ increase the air gap between the drum and the solidified shell to prevent the surface cracks of the slab by the gentle cooling action. The result is shown in FIG. FIG. 1 was obtained under the following conditions. First, using a twin-drum type continuous casting machine with a drum width of 1300 mm, a diameter of 1200 mm, and Ni plating on the surface,
The molten metal of steel type SUS304 is rapidly cooled and solidified, and the slab is 80 m.
It was drawn out at a speed of 1 / min to obtain a slab having a thickness of 2.3 mm.

On the surface of the cooling drum, 90% or more of the flat portion was formed with depressions by shot blasting. When a 0.15 mm depression is formed in this part,
The depression did not work as a solidification nucleus, and a crack was generated on the surface of the slab. Therefore, shot blasting was performed on the surface of the cooling drum under the following conditions. That is, using a pneumatic projection type blaster, the diameter is 0.15, 0.20, 0.25, 0.30,
A steel ball (martensite) of 0.35 or 0.40 and a diameter of 0.60, 0.65, 0.75, 0.85
A steel ball of either 0.90 or 1.10 mm is projected by air pressure;
The depressions were formed by changing the number ratio as shown in FIG. 2 by 3.6 to 10 kg / cm ² and the projection width of 20 mm per time.

A slab was manufactured under the same casting conditions as above using the cooling drum whose surface was processed as described above, and the amount of surface cracks generated on the obtained surface was investigated. As shown in Fig. 2, there are 5 dents of 0.4 mm or more in the area without cracks and uneven gloss.
It was found that the area was distributed at 0 to 200 pieces / cm ² , and was composed of dents of 0.3 mm or less, and 90% or more of the whole was engraved.

Here, if the diameter of the depression is larger than 1 mm, the portion corresponding to the depression after cold rolling remains as uneven gloss, so the range is 0.4 to 1.0 mm.

[0023]

EXAMPLE First, the continuous casting machine used in the present invention will be described with reference to FIG. 4. In the continuous casting machine, cooling drums 1 and 1 are arranged so as to rotate in parallel and in opposite directions. The side dams 2 and 2 are provided on both end faces of the molten metal to form the molten metal pool 4, and the molten metal 5 in the molten metal pool is cooled by the rotation of the cooling drums 1 and 1 to cast the thin cast slab S. There is. Further, the side dams 2 and 2 are pressed against both end surfaces of the cooling drums 1 and 1, and are kept in a sealed state by abrasion due to rotation of the cooling drums to prevent hot water leakage.

By changing the surface properties of the mold of such an apparatus as shown in Table 1, the composition of the stainless steel SUS304, the molten steel at a temperature of 1500 ° C., the wall thickness of 2.3 mm and the plate width of 800 mm at the casting speed of 80 m / min. The thin-walled slab was cast. NO 1-1 to 1-5 described in Table 1 are comparative examples, and NO
1-6 to 1-10 are examples of the present invention. As shown in Table 1, there is no fine crack on the surface of the cast piece cast by the method of the present invention,
Moreover, no uneven gloss was generated.

That is, solidification started from a large diameter portion of 0.4 mm or more, solidification uniformity in the cross-sectional direction was improved, and fine cracks could be eliminated. Further, by forming the depressions on almost the entire surface, unevenness of solidification in the large diameter portion and other portions can be reduced, and as a result, uneven gloss of the cold-rolled sheet can be eliminated. N
O1-1 and 1-2 have few large diameters of 0.4 mm or more,
Due to the small number of solidification starting points, the uneven solidification became excessive and fine cracks occurred. Also, NO1-3 is 0.4 mm
Although the number of the above depressions was proper, there were many flat portions on the drum surface, and uneven gloss occurred. Further, in NO1-4 and 1-5, large diameters of 0.4 mm or more were overlapped with each other to form a large group of dents, or streaks of dents were formed in the vertical direction, resulting in uneven gloss.

[0026]

As described above, according to the present invention, it is possible to form the recesses on the surface of the cooling drum in a distribution of the recesses without cracks and uneven gloss, and thus it is possible to reduce the processing period and cost. The industrial effect is great.

[Brief description of drawings]

FIG. 1 is a diagram showing the number of recesses of 0.4 mm or more, cracks in the area ratio of recesses on the drum surface, and the optimum range of uneven gloss.

FIG. 2 is a diagram showing an optimum range portion of a number ratio of a shot large diameter D ₁ and a shot small diameter D _{2 over} the number of dents of 0.4 mm or more.

FIG. 3 is a diagram showing a shape of a depression on a drum surface.

FIG. 4 is a perspective view of a twin-drum type continuous casting machine for carrying out the present invention.

[Explanation of symbols]

1 ... Cooling drum 2 ... Side dam 3 ... Molten metal discharge nozzle 4 ... Molten metal pool 5 ... Molten metal D ₁ ... Shot large diameter D ₂ ... Shot large diameter S ... Thin cast slab d ₁ ... Shot large diameter dent diameter d ₂ ... Small shot diameter dimple diameter l ₁ ... Shot large diameter dimple depth l ₂ ... Small shot dimple depth

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hidemaro Takeuchi 3434 Shimada, Hitsu-shi, Yamaguchi Yamada Pref., Komatsu Ltd. (72) Inventor Yasuo Matsubara 3434 Shimada, Hikari-shi, Yamaguchi Prefecture New Japan Hikari Steel Works, Ltd.

Claims (2)

[Claims] 1. The surface of a moving mold of a synchronous continuous casting device for thin cast pieces covers 90% or more of the peripheral area of the moving mold,
50 ~ per cm ² carved by shot blasting method
It consisted of 200 depressions having a circular or elliptical opening with a diameter of 0.4 to 1.0 mm and depressions with a diameter of 0.3 mm or less, and the remaining surface was composed of a flat portion with a surface roughness of 10 μm or less. A mold for continuous casting of thin-walled slabs. 2. The surface of a moving mold of a synchronous continuous casting apparatus for thin cast slabs having different diameters by a shot blasting method.
A surface processing method for a casting mold for continuous casting of thin cast slabs, characterized in that different types of steel balls are mixed and projected.