JPH0729185B2 - Cooling drum for thin strip continuous casting equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a twin-drum system, a single-drum system, and a drum-system.
The present invention relates to a cooling drum used in a belt type continuous thin band casting apparatus.

[Conventional technology]

In recent years, in the field of continuous casting of metals, for the purpose of cutting down manufacturing costs, creating new materials, etc., the development of technology for producing thin-walled slabs close to the final shape has been carried out. Among the continuous casting methods, equipment that has a relatively simple structure is used.Twin drum method that uses a pair of drums with internal water cooling mechanism as the main component of the mold, single drum that uses a single cooling drum. There are a drum system, a drum-belt system in which a hot water pool is formed between a cooling drum and a belt. In these casting methods, it is an important task to stably maintain the surface quality of the slab at a high level.

That is, the method of continuously casting these thin-walled slabs is different from the case of the slam produced by the conventional continuous casting equipment, in order to obtain a thin-walled slab capable of reducing the degree of rolling in the subsequent steps. For the purpose, if there is a variation in wall thickness or surface cracks in the thin cast slab, it becomes a defect on the surface of the product, and there is a great risk that the commercial value will be significantly impaired.

Therefore, various methods have been investigated for the purpose of stably producing a slab having good surface quality. As one of them, JP-A-60-184449 proposes to provide unevenness on the circumferential surface of the cooling drum so as to form an air gap that serves as a heat insulating layer between the cooling drum and the solidified shell. There is. Due to this air gap, the heat removal capability of the cooling drum is reduced, and the molten metal is cooled slowly.

As a result, it is said that the solidified thickness becomes uniform in the plate width direction, and it becomes possible to manufacture a thin cast piece having excellent shape characteristics.

[Problems to be Solved by the Invention]

However, by simply attaching irregularities of a specific depth to the peripheral surface of the cooling drum and maintaining it in the initial state,
It was found that sufficient effect could not be obtained stably. For example, when large irregularities are continuously provided on the peripheral surface of the cooling drum, irregularities are generated on the surface of the obtained thin cast slab, of course, concentration of thermal stress is promoted at that portion, and conversely cracking occurs. Is promoted. Further, when linear or angular irregularities are formed on the peripheral surface of the cooling drum, the corners of the irregularities serve as the starting points for cracking, causing numerous cracks in the thin cast piece.

Therefore, in order to solve these problems, the present inventors have
The unevenness formed on the peripheral surface of the cooling drum is examined,
A circular or oval opening having a diameter of 0.1 to 1.2 mm and a depth of 5 to 100 μm is formed on the peripheral surface of the cooling drum forming a part of the mold without contacting each other. The area ratio of the depression is periodically or independently changed in the axial direction and the circumferential direction of the cooling drum, the cycle w of the periodic change is 5 mm ≦ w ≦ 40 mm, and the change amount h of the area ratio of the depression is 10%. It was found that maintaining ≦ h ≦ 30% is effective, and the application was filed as Japanese Patent Application No. 63-202962.

In this way, the recess provided on the peripheral surface of the cooling drum is
By forming independent air gaps that are not continuous during casting, the cooling conditions of the solidified shell are relaxed and the partial concentration of stress is suppressed, but by giving a periodical change to the distribution of the above-mentioned depressions, the shell The solidified shell is grown so as to cancel out the variation in thickness.

However, as a result of subsequent research, when the area ratio of the depressions of the cooling drum was periodically changed in the circumferential direction (vertical direction) and the axial direction (horizontal direction) of the cooling drum, the depressions became the longitudinal direction and the lateral direction of the cooling drum. Alternatively, it was confirmed that the parts arranged in a line in a diagonal direction were formed, and cracks were generated on the surface of the slab from the parts having this directionality.

Therefore, an object of the present invention is to produce a thin cast piece which is free from defects such as cracks and has excellent surface properties and shape characteristics by further improving the distribution of the depressions provided on the peripheral surface of the cooling drum.

[Means for Solving the Problems] In order to achieve the object, the cooling drum for a ribbon continuous casting apparatus of the present invention has a depth of 5 to 100 μm and a diameter of 0.1 to 1.2 mm.
A circular or oval opening having a circular opening is formed at a non-directional position in the longitudinal direction, the lateral direction and the oblique direction of the peripheral surface of the cooling drum which constitutes a part of the mold, and the area of the depression. The rate is changed independently or simultaneously in the longitudinal direction and the transverse direction of the cooling drum, and the period w of the periodic change is
5 mm ≤ w ≤ 40 mm, change amount h of the area ratio of the depression is 10% ≤
It is characterized in that h ≦ 30% is maintained.

[Action]

In the present invention, the area ratio of the depressions provided on the peripheral surface of the cooling drum for casting the thin cast piece has a predetermined cycle (second
(See FIGS. 2 (B) and (C)), since each of the depressions is provided at a position having no directivity in the longitudinal direction, the lateral direction, and the oblique direction with respect to the peripheral surface of the cooling drum (see FIG. 2 (A)), The cycle of the thick and thin portions of the solidified shell generated on the peripheral surface of the cooling drum is controlled to cancel variations in the shell thickness, and slab cracking due to the directionality of the depression is prevented, resulting in a high quality product.

It should be noted that the shape of the depression is 5 to 100 μm in depth and 0.1 to 1.2 mm in diameter.
The reason why the shape having a circular or oval opening is specified is as follows.

That is, according to the experiments by the present inventors, the diameter of the depression is 0.
If it is less than 1 mm, not only the effect of slow cooling is small, but also cleaning is difficult, it is easily affected by scratches and wear on the drum surface, and processing is also difficult. On the other hand, if the diameter of the dent exceeds 1.2 mm, the dent itself tends to be the starting point for microcracks, and molten metal penetrates into the dent, and numerous fine projections are generated on the surface of the thin cast piece obtained. . If the depression is shallower than 5 μm, the heat insulating effect of the air gap formed therein is significantly reduced, and the slow cooling effect is reduced. On the other hand, 100
Opening diameter 1.2m for depressions with a depth exceeding μm
No increase in effect was observed as far as depressions of m or less were observed.

In addition, it is an experimental fact that, in many cases, the period w of the depression shown in FIG. 1 is set to 5 to 40 mm and the variation h of the area ratio is set to 10 to 30%. In order to forcibly cancel the waviness in this range by the change in the depression formed on the peripheral surface of the cooling drum, at least two depression changes should exist in the deformation mode of the solidification shell. This is due to the reason that it became clear that there was no effect. Further, regarding the area ratio, the effect was reduced even if the difference was too small, and it was found that the range of 10 to 30% was optimal. On the other hand, the relationship between the period w of the depression and the change amount h of the area ratio is mainly a regular arc function, but in the present experimental results, there is no significant difference even if the continuous function is deviated from the regular arc function. Was confirmed.

In addition, arranging the depressions in a non-directional position means that when the depressions are engraved on the peripheral surface of the cooling drum, the cooling drum has a longitudinal direction (cooling drum circumferential direction) and a lateral direction (cooling drum axial direction). In addition, since the depressions are not aligned in a line in the oblique direction, it is assumed that there is directionality when at least five adjacent depressions are linearly arranged.

That is, when five or more adjacent dents are arranged in a straight line, the slab is cracked from the group of the dents. In this way, if the recessed position is specified as described above at a predetermined cycle, cracking of the steel piece hardly occurs.

Hereinafter, the present invention will be described with reference to examples.

〔Example〕

A thin cast piece was produced from molten steel having a stainless steel composition by the apparatus shown in FIG. That is, the molten steel 4 having a temperature of 1500 ° C. poured from the tundish 5 through the pouring nozzle 2 into the molten metal pool 3 is rapidly cooled and solidified between the pair of cooling drums 1a and 1b, and the solidified shell formed is kissed. Pressed at point 6 and casted at a speed of 65 m / min, wall thickness 2.4 mm, plate width 800
mm thin cast slab 7 was produced.

At this time, the pair of cooling drums 1a and 1b are a cooling drum having a distribution of depressions on the peripheral surface of the cooling drum of the present invention (FIG. 1A) and a cooling drum having a distribution of depressions of a comparative example (first
The surface condition of the obtained thin cast piece 7 was measured by using two types of cooling drums shown in FIG.

In the example of FIG. 1 (C), the area ratio of the depression is periodically changed from 25% at maximum to 15% at minimum (wave height h = 10%) at a cycle w of 15 mm in the lateral direction of the cooling drum. Directionality was formed in the lateral direction at the joint of the change in the cycle.

On the other hand, in the example of FIG. 1 (A), the depressions are engraved in the same distribution as in FIG. 1 (C), and the joints of the changes in the cycle are arranged as shown in the figure, in the vertical direction, the horizontal direction, and the diagonal direction. Lost the omnidirectionality of all directions.

In each of FIGS. 1 (A) and 1 (C), one depression was engraved so as to have a circular opening having a depth of 30 μm and a diameter of 0.5 mm.

Table 1 shows the occurrence of slab cracking depending on the type of cooling drum. The crack initiation index is represented by the length of vertical crack (m) per 1 m ^{2 of} casting area.

As is clear from Table 1, in the known example in which the depressions having a circular opening with a depth of 30 μm and a diameter of 0.5 mm are evenly distributed, 2
Cracks occurred in the range of up to 3 m / m ² . Further, the crack occurrence rate of the comparative example was reduced to 1 or less as compared with the known example, but some crack occurrence could not be avoided yet.

On the other hand, in the example of the present invention, the occurrence of cracks could be substantially eliminated.

〔The invention's effect〕

As described in detail above, the present invention gives a periodic change in the area ratio of the depressions formed on the peripheral surface of the cooling drum, and eliminates the mutual directionality of the depressions, so that defects such as cracks on the surface of the slab are substantially eliminated. However, it has become possible to manufacture thin cast slabs having extremely excellent surface properties.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the period w of the depressions engraved on the peripheral surface of the cooling drum and the change amount h of the area ratio, FIG. 2 shows an example of the depression distribution, and FIG. 3 shows this cooling. It is the schematic which shows the thin strip continuous casting apparatus which incorporated the drum. 1a, 1b ... Cooling drum, 2 ... Pouring nozzle, 3 ... Hot water pool,
4 ... Molten metal, 5 ... Tundish, 6 ... Kissing point, 7 ... Thin cast piece, 8 ... Pinch roll.

Front page continuation (72) Inventor Mitsuru Nakayama 1-3-1 Makiyama, Tobata-ku, Kitakyushu, Fukuoka Inside Hamada Heavy Industries Co., Ltd. (72) Keiichi Yamamoto 4-6-22 Kannon-Shinmachi, Nishi-ku, Hiroshima City Heavy Industry Co., Ltd. Hiroshima Laboratory (72) Inventor Takashi Yamane 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Ltd., Hiroshima Laboratory

Claims (1)

[Claims] 1. A dent having a circular or oval opening having a depth of 5 to 100 μm and a diameter of 0.1 to 1.2 mm is formed in a longitudinal direction, a lateral direction and a longitudinal direction of a peripheral surface of a cooling drum forming a part of a mold. It is formed in a position having no directivity in an oblique direction, and the area ratio of the recess is periodically or independently changed in the longitudinal direction and the transverse direction of the cooling drum, and the cycle W of the cyclic change is 5 mm.
≦ W ≦ 40 mm, the change amount h of the area ratio of the depression is 10% ≦ h ≦
Cooling drum for thin strip continuous casting equipment characterized by maintaining at 30%.