JPH0452053A - Cooling drum for continuously casting metal strip - Google Patents

Abstract

PURPOSE:To obtain a strip having surface without any crack, breakage, uneven gloss, etc., by forming round recessed parts having the specific diameter, depth and inclination angle on surface of cooling drum to relax cooling condition. CONSTITUTION:Molten metal is poured into pouring basin part 3 demarcated with one pair of the cooling drums 2 and side weirs 4 from an intermediate vessel of a tundish 1, etc. The poured molten metal is cooled and solidified with heat conduction of the cooling drums 2 on the surface thereof. Solidified shells formed on the surfaces of cooling drums 2 are shifted downward according to rotation of the cooling drums 2 and welded under pressing with roll gap part and fed out from between the cooling drums 2 as one piece of the cast strip 5. This cast strip 5 is conveyed toward pinch rolls 6 while drawing the loop. Then, on the surface of cooling drum contact with molten metal in the pouring basin part 5, the recessed parts having round or oval shaped opening parts of 0.1-1.2mm diameter and 5-50mum depth and 90 deg.-150 deg. average inclination angle of the recessed part, are closely arranged without mutually contacting.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a continuous casting apparatus such as a twin-drum type, single-drum type, or drum-belt type for directly producing a ribbon from molten metal, and particularly relates to a continuous casting apparatus such as a double-drum type, single-drum type, or drum-belt type. This relates to the shape of the depression on the surface of the cooling drum in the device.

[Conventional technology]

The conventional method for manufacturing thin plates using continuous casting is to cast a slab with a thickness of 100 mm or more while vibrating the mold in the casting direction, then treat the surface of the resulting slab and heat it in a heating furnace. After that, it is hot rolled using a hot strip mill consisting of a rough rolling mill and a finishing mill row to form an IJ tube (thickness number), and then annealed if necessary, descaled and cold rolled. Final annealing was performed.

In such a conventional process, a thickness of 100 II
II [There was a problem in that a long hot strip mill was required to hot-roll one or more slabs, and a large amount of energy was used to heat and roll the slabs.

In order to solve this problem, research is underway into a process for producing slabs with a thickness equal to or close to that of hot strip by continuous casting. For example, "Tetsu to Hagane J
A synchronous continuous casting process with no relative speed difference between the slab and the inner wall of the mold, such as the twin-drum method and the twin-belt method, as introduced in the papers featured in '85-A197~'85-A256. be.

However, unresolved issues remain in manufacturing thin sheet products through these synchronous continuous casting processes.

In other words, when manufacturing a thin plate using a continuous casting process to produce a slab (thin strip slab) with a thickness equal to or close to that of hot strip,
There was a problem with the surface quality of the product.

Therefore, various methods have been investigated with the aim of stably producing slabs with good surface quality.

One of them is to provide unevenness on the circumferential 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.
It is proposed in the publication. This air gap allows
The heat removal capacity of the cooling drum is reduced, and the molten metal is cooled slowly. As a result, the solidified thickness is made uniform in the plate width direction, making it possible to manufacture thin slabs with excellent shape characteristics.

[Problem to be solved by the invention]

However, when casting with irregularities of a certain depth on the circumferential surface of the cooling drum, an abnormal structure is generated on the surface of the resulting slab, which may cause uneven gloss on the surface of the cold-rolled steel sheet. understood.

The present invention uses a cooling drum with unevenness on its circumferential surface to produce a metal thin strip, and the metal ribbon has excellent shape characteristics and does not have abnormal structures that cause uneven gloss on its surface. The purpose is to provide thin strips.

[Means to solve the problem]

To achieve this objective, the present invention provides a cooling drum with a circular shape on its surface, which has a diameter of 0.1 to 1.2 mm, a depth of 5 to 50 squares, and an average slope angle of the sides in the range of more than 90 to 150 degrees. Alternatively, it is characterized in that depressions with oval openings are formed without touching each other.

[For production]

The cooling drum of the present invention has a large number of circular or oval depressions formed on its surface. When a solidified shell is formed on the surface of the cooling drum, the depressions form independent air gaps that are not continuous with each other. Therefore,
The high-temperature parts, which have been slowly cooled by the air gap and are still in a state of low rigidity, are not continuous on the surface of the solidified shell, but are separated from each other. This is surrounded by a highly rigid portion that is sufficiently cooled by direct contact with the cooling drum.

As a result, the thermal stress concentrated in areas with low rigidity becomes small, and since those areas are in an independent state, cracks due to contraction of the solidified shell will not occur across multiple low-rigidity areas. Of course, the occurrence of cracks is suppressed even in a single portion where the rigidity is decreased.

In this way, the cooling conditions of the solidified shell are relaxed by forming the depressions, and the adverse effects caused by stress concentration in a region where the rigidity is locally low are suppressed.

However, as shown in Figure 9, when looking at the structure of the slowly cooled part (B) of the solidified shell, the amount of δ-ferrite is larger than that of the non-slowly cooled part (A), and this difference in structure is due to the final It was found that this caused uneven gloss on the product.

In order to eliminate the above-mentioned uneven gloss, when descaling the slab surface by pickling or the like, it is necessary to reduce the depth to about 1001 m or less, which is enough to remove the above-mentioned abnormal tissue together.

The present inventor obtained the following results by investigating the relationship between the depth and shape of the depressions on the surface of the cooling drum and the depth of the δ-ferrite structure generated in the depressions.

In Figure 1, the average inclination angle of the side surface connecting the upper edge C and the bottom of the recess 7 shown in Figure 3 (hereinafter referred to as the recess average inclination angle (θ)) is over 90°, and the recess depth on the cooling drum surface is E(p)
This figure shows the relationship between the depth F (Rn) of the δ-ferrite structure on the surface of the slab as shown in Figures 5 and 8, which is caused by this depression. Below, the depth F of the δ-ferrite structure suddenly becomes shallow, and when the depression depth E is 50Ia, the depth F of the δ-ferrite structure is lQ.
It turns out that Q is less than a.

Note that if the depth of the depression is less than 5 Jm, the effect of slow cooling by the depression will be insufficient, the stress dispersion effect during solidification will be lost, and microcracks will occur in the slab, making it difficult to achieve the intended purpose of the present invention. I can't.

If the diameter of the recess opening is less than Gi:J<0.1 mm, not only will the slow cooling effect be small, but it will also be difficult to clean, easily affected by scratches and dirt on the drum surface, and difficult to process. On the other hand, when the diameter G of the recess opening exceeds 1.2 mm, the recess itself tends to become a starting point for micro-cracks, and molten metal enters the recess, resulting in a large number of microscopic cracks on the surface of the obtained thin slab. Protrusions are formed and the surface quality of the slab is unfavorable.

Figure 2 shows the relationship between the average depression angle (θ) and the depth F of the δ-ferrite structure. This figure shows the depth F of the δ-ferrite structure at that time.

According to this, it can be seen that in order to make the δ-ferrite structure depth F less than about 100 pores below the surface depth removed during the descaling process, the average inclination angle (θ) of the depressions should be set to more than 90°.

Furthermore, when the average inclination angle θ of the recess exceeds 150°, the heat insulation effect due to the air gap formed on the bottom of the recess is significantly reduced, the stress dispersion effect during solidification is lost, and microcracks occur in the thin slab.

Therefore, in order to maintain the warming and cooling effect of the depressions on the surface of the cooling drum and to prevent uneven gloss due to the 5δ-ferrite structure, the diameter G of the depression opening is set in the range of 0.1 to 1.2 mm, and the depression depth E 5~50I! rIl, and the average inclination angle θ of the depressions needs to be in the range of more than 90° to 150°.

As the recess opening, in addition to the circular shape, an elliptical shape and a combination of a circular shape and an elliptic shape are also used.

When the opening is oval, both the short axis and long axis are 0.
．． The thickness should be in the range of 1 to 1.2 mm. In this sense, the diameter of the recess opening in this specification includes the short axis and long axis.

Also, Fig. 3 (b), (cl), (e), (
As shown in f), the occurrence of uneven gloss can be further prevented by rounding the corners (upper edge and bottom) of the recess and giving them a curvature. That is, if the upper edge of the recess is sharp, this portion locally contacts the shell and is strongly cooled. Further, if the bottom of the depression is locally concave, the shell is locally slowly cooled. This promotes the occurrence of texture unevenness, that is, uneven gloss. On the other hand, if the upper edge of the recess has a curvature, this portion will be in continuous contact with the shell and will not be locally strongly cooled. Further, unless the bottom of the depression is locally concave, the shell will not be locally slowly cooled.

This suppresses the occurrence of texture unevenness, that is, uneven gloss.

〔Example〕

Hereinafter, the features of the present invention will be specifically explained using examples with reference to the drawings.

FIG. 10 shows a twin-drum continuous casting machine to which the present invention is applied.

Molten metal is poured from an intermediate container such as a tundish 1 into a sump 3 partitioned by a pair of cooling drums 2 and a side weir 4. The injected molten metal is cooled and solidified on the surface of the cooling drum 2 as the heat is removed. In this way, the solidified shells formed on the surface of each cooling drum 2 move downward as the cooling drum 2 rotates, are crimped at the roll gap, and form -thin slabs 5 on the cooling drum. It is sent out from between 2. This thin slab 5 is
It is conveyed toward the pinch roll 6 while drawing a loop.

At this time, the surface of the cooling drum 2 that comes into contact with the molten metal in the pool 3 has a circular or oval opening with a diameter G of 0.1 to 1.2 mm, and a depth E of 5 to 50 mm. Sir, the depression 7 with an average inclination angle (θ) of more than 90° to 150° is
They are densely arranged without touching each other.

FIG. 3(b) is an enlarged sectional view of an example of the depression, which has a circular opening with a diameter G of 0.3 mm, a depth of 207°, and an average inclination angle θ of 110°. It shows a depression 7 consisting of. In this cooling drum 2, steel composition (weight%) Co O, 06%, Si 0.45%, Mn1
．． 21%, SO,001%, P0003%,
When molten steel containing 9.50% Ni, 18.5% Cr, and the balance Fe was cast, the shape of the slab surface corresponding to the above-mentioned depressions of the slab 5 was similar to the depression opening as shown in FIG. Correspondingly, it has a dish-shaped raised shape, and the metal structure in its cross section is shown in Figure 5, where the abnormal area H has a structure containing 8% δ-ferrite at a depth of about 1001 mm! m occurred. The amount of δ-ferrite contained in the metal structure of the part I between the depressions was about 1%.

As described above, when a ribbon is cast using the cooling drum having depressions according to the present invention, the surface depth of about 100 mm is removed by the descaling treatment after casting, so almost all of the δ-ferrite structure can be removed. I can do it.

As a comparative example, FIG. 6 shows a cooling drum 2 having a recess 8 having a circular opening with a diameter of 0.3 mm, a depth of 30, and an average inclination angle of θ90°. An example of casting is shown. The slab shape shown in Fig. 7 has a dish-like bulge from the narrow opening compared to Fig. 4, and in the metal structure shown in Fig. 8, the depth of the δ-ferrite structure in the abnormal area H is about 300μ. As a result, it penetrated deeper than in FIG. 5, and could not be completely removed by descaling, causing uneven gloss.

As described above, when the ribbon 5 is manufactured using the cooling drum 2 having the recesses 7 formed on the surface of the present invention, it is possible to ensure the air gap effect and prevent the defects of microstructural non-uniformity due to uneven cooling. .

〔Effect of the invention〕

As explained above, in the present invention, by forming circular depressions having a predetermined inclination angle on the surface of the cooling drum, the cooling conditions are relaxed and the surface texture is smooth and crack-free. A thin slab is produced in which the δ-ferrite structure generated by relaxation is made as shallow as possible. Therefore, by the subsequent descaling treatment and rolling process, it is possible to obtain a ribbon having excellent surface properties without cracks, breaks, uneven gloss, etc.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the depression depth on the cooling drum surface and the depth of the δ-ferrite structure, Figure 2 shows the relationship between the depression inclination angle on the cooling drum surface and the δ-ferrite structure, and Figure 3 shows the relationship between the depression inclination angle and the δ-ferrite structure on the cooling drum surface.
The figure is an enlarged sectional view of the depressions on the surface of the cooling drum of the present invention.
The figure is an enlarged sectional view of the slab portion corresponding to the depression in Figure 3, Figure 5 is a diagram showing the metallographic structure of the slab part in Figure 4, and Figure 6 is an enlarged view of the depression on the surface of the cooling drum of a comparative example. 7 is an enlarged sectional view of the slab portion corresponding to the depression in FIG. 6, FIG. 8 is a diagram showing the metallographic structure of the slab portion in FIG. 7, and FIG. 9 is a diagram showing the δ- A perspective view schematically showing a ferrite structure, 1st
FIG. 0 is a schematic front view showing a twin-drum type continuous casting machine incorporating the cooling drum of the present invention. 1... Tanditetsu, 2... Cooling drum, 3
... Hot water pool, 4°°° side weir, 5...
Thin slab, 6...pinch roll. Depth of the depression on the surface of the cooling drum (μm) First factor Inclination angle of the depression on the surface of the cooling drum (θ) Fig. 2 Fig. Fig. 9 4.Side weir 5-Thin slab 6 Pinotero

Claims (1)

[Claims] 1. Diameter is 0.1 to 1.2 mm, depth is 5 to 50 μm,
For continuous casting of metal ribbon, characterized in that depressions with circular or elliptical openings whose side faces have an average inclination angle of more than 90° to 150° are formed on the surface of the cooling drum without touching each other. cooling drum.