JPS6238069B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a horizontal continuous casting method capable of casting slabs without cold shell cracks.

In recent years, the continuous casting method has been rapidly developing because it is superior to the ingot-forming method in terms of yield, energy saving, etc. As shown in Fig. 1, the molten steel poured from the ladle 1 into the tundish 2 is
The horizontal continuous casting method, in which slabs 5 are cast by horizontally pulling the slabs from a mold 4 that is horizontally fixed to the lower part of the side wall of the tundish 2 via the nozzle 3, is different from the vertical continuous casting method, in which the slabs are pulled out from the lower part of the mold. It is attracting attention because of its lower construction costs, easier maintenance, and the ability to produce slabs with high cleanliness.

In the horizontal continuous casting machine, unlike the vertical continuous casting machine, the mold and the tundish are completely connected by a nozzle. For this reason, when performing mold oxidation, which is normally performed in vertical continuous casting to prevent the solidified shell from sticking to the inner surface of the mold, in horizontal continuous casting,
It is necessary to vibrate the mold and tundish at the same time, which requires large-scale equipment, and the refractory used to join the nozzle, mold, and tundish can't withstand vibrations, so mold oscillation is difficult. It is difficult to carry out horizontal continuous casting method.

For this purpose, in the horizontal continuous casting method, the mold is fixed, and as shown in Figure 2A, the slab is pulled out of the mold for a certain period of time, then pushed back in the opposite direction to the drawing direction for a certain period of time, and then again. The slab is repeatedly pulled out from the mold for a certain period of time, or as shown in Figure B, the slab is pulled out from the mold for a certain period of time, stopped for a certain period of time, and then pulled out again for a certain period of time. A repeated, intermittent extraction method is used.

When the above-mentioned intermittent drawing is performed, a different solidification form is observed than when the slab is continuously drawn as in the vertical continuous casting method. This will be explained below.

As shown in FIG. 3, a portion of the molten steel 6 supplied into the mold 4 from a tundish (not shown) that comes into contact with the inner surface of the mold 4 immediately solidifies to form a shell 7. This shell 7 gradually grows because the mold 4 is cooled. On the other hand, a break ring 8 is attached to the molten steel inlet end of the mold 4. This break ring 8 is cooled because it is in contact with the mold 4. For this reason, the portion of the molten steel 6 supplied into the mold 4 that comes into contact with the break ring 8 also solidifies, albeit slightly. Solidification also progresses through the shell 7' formed by drawing in the previous step.

Therefore, the joint 9 between shell 7 and shell 7'
has a structure different from that of other shell parts, that is, a structure called a cold shell (C, S). Normally, this cold shaft is completely welded, but if the joint 9 is cooled too much,
Cold-shut crack without welding (C, S,
A crack called C) occurs.

The above-mentioned cold shut and cold shut crack have a strong correlation with the drawing cycle of the slab. This relationship is shown in FIG. As is clear from Fig. 4, the higher the pulling cycle, the more the growth of the cold shaft tissue is suppressed;
The cold-shuttle truck has a pull-out cycle.
It can be seen that it becomes almost zero at 120 cycles/min or more. That is, as the drawing cycle becomes higher, the shell thickness of the first shell 7 becomes thinner, so that the growth of the cold shell structure is suppressed and its height becomes lower. Furthermore, since the temperature at the shell joint portion 9 becomes high, weldability is improved and the occurrence of cold shell cracks is prevented.

However, drawing at such high cycles requires advanced control technology, and in the case of square billets, the corners are cooled from two directions of the mold, as shown in Figure 5. It is supercooled compared to other parts. For this reason, there was a problem in that even if drawing was performed at a high cycle as described above, it was not possible to completely prevent cold shut cracks occurring at the corners.

The cold shutter crack above has a depth of 0.2
Since it is a slight crack of about 0.5 mm, it will disappear when rolled into a round bar, shaped steel, wire rod, etc.
However, when the rolling reduction is small, for example, when rolling into a thick round bar, scratches remain on the surface of the product. Of course, these surface flaws can be removed by performing care before rolling, but this leads to a decrease in yield and is very time consuming.

From the above-mentioned viewpoints, the present invention provides a horizontal continuous casting method capable of obtaining slabs that do not cause cold shatter cracks even when drawn at a low cycle. In the horizontal continuous casting method in which a slab is cast by intermittent drawing, the intermittent drawing of the slab is performed at 30 cycles/min or more, and the unsolidified slab is heated to a high temperature. It is characterized by projecting a shot ball toward a surface that has a surface.

This invention will be explained by way of examples and with drawings.

FIG. 6 is a block diagram of an embodiment of the present invention.

As shown in FIG. 6, the method of this invention:
Shot balls (not shown) are projected from a shot ball projection device 11 installed downstream of a spray cooling device 10 toward a slab 5 that is intermittently pulled out from a mold 4. In FIG. 6, 2 indicates a tundish, 3 a nozzle, 4 a mold, and 12 a pinch roller.

The shot ball projection device 11 continuously projects steel shot balls with a diameter of about 1.4 mm toward the surface of the slab at a speed of about 70 m/sec.

As the shot balls collide with the surface of the slab, the surface layer of the slab is lightly reduced, thereby removing the cold shatter cracks present on the surface of the slab 5.

FIG. 7 shows the relationship between the drawing cycle and the depth index of the cold shaft cracks (C, S, C).

As is clear from Fig. 7, when the shot balls are projected onto the surface of the slab, the drawing cycle is 30 cycles/
It can be seen that cold shutdown cracks do not occur even when running at a low cycle of mln.

As explained above, according to the present invention, even if the slab is drawn intermittently at a low cycle, it is possible to obtain a slab without cold shatter cracks, thereby eliminating the trouble of cleaning the slab. It is possible to save labor and to easily control the drawing of slabs. Moreover, since there is no need for maintenance of the slab, it is possible to carry out so-called hot direct rolling, which has been attracting attention recently, in which the hot slab is directly conveyed to the rolling process without being cooled and rolled. Various useful effects are brought about, such as ease of implementation.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the horizontal continuous casting method, Fig. 2 is a diagram showing the method of drawing slabs, Fig. 3 is a partial cross-sectional view showing the state of forming a shell, and Fig. 4 is a drawing cycle C. , S and C, S, and C. FIG. 5 is a diagram showing the position of a cold shaft crack that occurs in a corner billet. FIG. 6 is an explanatory diagram of an embodiment of the present invention. FIG. 7 is a diagram showing the relationship between the drawing cycle and the depth index of C, S, and C. In the drawings: 1...Ladle, 2...Tundish, 3...Nozzle, 4...Mold, 5...Slab, 6... Molten steel, 7,7'...Ciel, 8...Break ring, 9 ... Seam part, 10 ... Spray cooling device,
11... Shot ball projection device, 12... Pinch roller.

Claims (1)

[Claims] 1. In a horizontal continuous casting method in which slabs are cast by intermittently pulling slabs from a mold, the intermittent pulling of the slabs is 30 cycles/min or more, and the unsolidified cast that has been pulled is A horizontal continuous method characterized by projecting a shot ball onto the heated surface of the slab and thereby obtaining slabs without cold shot cracks even during intermittent drawing at low cycles. Casting method.