JPH02263543A - Method for continuously casting strip - Google Patents

Abstract

PURPOSE:To obtain a cast strip having sound surface characteristic and inner quality by continuously supplying molten metal to a cooling body and further, spraying drip-state semi-molten metal on the surface opposite to the cooled surface of the cast strip, which is being solidified from one direction with the cooling body. CONSTITUTION:The cooling body 1 as the rotating roll is set at opening end part of one side of a molten metal vessel, and by rotating the cooling body 1, the strip casting layer 20 is formed on the surface thereof. On the formed strip casting layer 20, the semi-solid state dripped molten metal is sprayed to form the spray casting 21 on the upper surface of the strip casting layer 20. By this method, the cast strip having sound surface characteristic and inner quality is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for continuously casting thin slabs with sound surface and internal quality.

(Prior Art) Generally, metal sheets are manufactured by first manufacturing continuous casting slabs or blooming rolled slabs from molten metal, and then hot rolling and cold rolling them.

However, if it were possible to continuously cast slabs several mm thick directly from molten metal, it would be possible to omit the hot rolling, and a significant reduction in equipment and energy costs would be expected. Ru. Therefore, in recent years, many technological developments have been made for this purpose.

One method for this is to bring the molten metal into contact with a moving cooling body and cool and solidify it from one direction. A specific example of this method is shown in FIGS. 6, 7, and 8.
As shown in the figure.

6 and 7 show a method of casting a thin slab 3 from molten metal 4 by direct solidification (hereinafter referred to as "strip casting method"), and FIG. Blow gas 8 to turn molten metal 4 into droplets 10,
In addition, it is a method (hereinafter referred to as "spray casting method") of casting a thin slab 3 in a semi-solidified state by collecting it on a cooling body 1 and solidifying it from one direction.

In addition, the arrow 2 in FIGS. 6 to 8 indicates the casting direction, and the arrow 5
Reference numeral 4 indicates a supply nozzle for molten metal, 6 indicates a refractory expansion, 7 indicates a droplet layer atomizing gas supply nozzle, and 9 indicates a sealing chamber.

(Problem to be solved by the invention) Problems with the above-mentioned prior art are as follows.

(1) In the strip casting method shown in Figs. 6 and 7, the surface of the slab in contact with the cooling body (hereinafter referred to as the "slab cooling surface J") has a relatively good surface quality. Irregularities occur on the surface that does not come into contact with the cooling body (hereinafter referred to as "slab cooling surface J"), and minute voids are generated directly below this casting slab cooling surface.

Since these pores exist directly below the cooling surface of the slab, slight deformation of the slab during casting may cause cracks, which cause surface defects on products after cold rolling. Furthermore, even if the slab does not have cracks, it may break or lose its product value starting from the voids during cold rolling.

(2) In the spray casting method shown in FIG. 8, the voids seen in the strip casting slab are not observed, but the surface quality of the cooling surface of the slab is poor.

It is an object of the present invention to solve the problems of the prior art described above and to provide a method for continuously casting thin slabs with good surface quality and no micropores inside the slab.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for continuously casting thin slabs by cooling and solidifying molten metal from one direction. At the same time, the molten metal is further sprayed in the form of semi-molten droplets onto the non-cooled surface of the slab, which is being solidified from one direction by the cooling body.

That is, the present invention makes it possible to compensate for and improve the shortcomings of both strip casting and spray casting by using them together.

(Function) First, before explaining the function of the method of the present invention, the mechanism of generation of micropores generated in a thin slab by the strip casting method will be explained.

For thin slabs produced by strip casting method,
As shown in Figure 9 (a), solidification progresses from the cooling body,
The final solidification becomes the cooling surface 13. However, the slab immediately after coming out of the molten metal bath is cooled not only from the cooling surface 12 side but also from the cooling surface I3 side by convection and radiation heat transfer by the atmosphere or atmospheric gas, and the surface solidifies. Therefore, the ninth
The volume reduction that occurs when the molten steel solidifies between the dendrite trees 14 shown in Figure (A) is not replenished by molten metal, and voids 16 are generated when the molten steel completely solidifies (Figure 9). (B)).

These holes 16 are formed directly below the cooling surface 13, so when a deforming force is applied to the slab (for example, during winding),
Easily cracks. In addition, even if cracks do not occur, holes are opened starting from the holes 16 during cold rolling,
This results in so-called blemishes on the product after rolling. In addition, the 9th
In the figure, arrow 11 indicates the direction of solidification progress, and 15 indicates residual molten steel between dendrite trees 14.

On the other hand, in spray casting slabs, semi-solidified droplet metal is brought into contact with a cooling body, so the initial droplets are rapidly cooled and solidified by the cooling body. For this reason, the initial droplet 18
are not sufficiently bonded to each other, and completely solidify with voids F remaining between the droplets on the slab cooling surface 12 (see FIG. 10). These holes 17 cause blemishes during cold rolling.

However, inside the slab, the droplets are easily deformed because the cooling is slow, and the high temperature allows the droplets to sufficiently bond with each other. No micropores are generated. Here, the semi-solidified state means that the in-phase rate is 1% or more and 100% or less,
A state in which the average temperature is below the liquidus temperature and above the solidus temperature.

Note that 19 in FIG. 10 indicates a droplet that has been completely combined and solidified.

Therefore, heating the cooling body is an effective method for improving the properties of the cooling surface of spray casting slabs, but it is not easy to heat the cooling body, which moves at high speed, quickly and without deformation.

Therefore, in the present invention, the slab obtained by the strip casting method is used as a cooling body in the spray casting method, and the droplets obtained by the spray casting method and the strip casting slab are combined to form one thin slab. It is something.

In this case, it is desirable to apply spray casting while the cooled side of the strip casting slab is as hot as possible, ie, immediately after being pulled out of the molten metal bath. According to the inventor's experimental results, the strip casting slab could be cast successfully if the surface temperature was within 100°C lower than the liquidus temperature of the metal.

Under this condition, the atomized droplet metal was completely bonded to the strip casting slab. In addition, the minute voids found just below the cooling surface of the strip casting slab were compressed by the semi-solidified high-temperature droplets supplied from above, and completely disappeared in the final solidified state. The cooling surface of the slab was obtained by strip casting and had good surface quality.

In this way, by using the strip casting method and spray casting together, it is possible to compensate for and improve the shortcomings of both methods. This makes it possible to continuously cast thin slabs.

In addition, 20 in FIG. 4 is a strip casting layer, 2
1 indicates a spray casting layer.

(Example) The method of the present invention will be explained below based on the example shown in FIGS. 1 to 3.

Note that in FIGS. 1 to 3, the same numbers as in FIGS. 6 to 8 indicate the same or corresponding parts, and detailed explanations will be omitted.

Figures 1 to 3 all show examples of application of the method of the present invention, but each differs only in the strip casting method, which is the earlier step of the method, and the spray casting method, which is the later step, is the same. be.

That is, in FIG. 1, a refractory weir 6 is provided on the surface of a cooling body 1 that is pulled up obliquely, and molten steel 4 is supplied from a supply nozzle 5 into the space formed by this refractory weir 6 and the cooling body 1 for cooling. The molten metal 4 is cooled from the surface of the body 1 to form a strip casting layer 20 on the surface.

Further, in FIG. 2, a cooling body 1, which is a rotating roll, is installed at one open end of the molten metal container, and a strip casting layer 20 is formed on the surface of the cooling body 1 by rotation of the cooling body 1.

Further, in FIG. 3, the lower end of a cooling body 1, which is a rotating roll, is immersed in a molten metal container, and the rotation of this cooling body 1 forms a strip casting layer 20 on its surface.

Then, on the strip casting layer 20 formed as shown in FIG. 1 to FIG. A layer 21 is formed.

Next, the results of casting using Fe-based and Ni-based alloys as molten metals by the method shown in FIG. 3 will be described.

The casting conditions were as shown in Table 1, and the obtained slabs were cut to investigate the occurrence of internal pores and the bonding state between the strip casting layer and the spray casting layer.

Figure 5 shows the occurrence of pores inside the slab, and it shows that the temperature of the cooling surface of the strip casting slab is 10° below the liquidus temperature.
When the temperature is below 0°C, there are no pores,
It was found that the bonding between the spray casting layer and the strip casting layer was also satisfactory.

In addition, the obtained slabs without internal pores were subjected to surface pickling and then directly cold rolled to produce products with a thickness of 0.8M, and in both cases, good steel plates with no surface flaws could be obtained. .

In this example, Fe-based and Ni-based alloys have been described, but it is clear that the present invention can also be applied to casting of other molten metals.

Table 1 is a schematic cross-sectional view of slabs manufactured by the spray gearing method.

1 is a cooling body, 4 is a molten metal, 10 is a droplet, 20 is a strip casting layer, and 21 is a spray casting layer.

(Effects of the Invention) As explained above, according to the method of the present invention, it is possible to continuously cast thin slabs with a healthy surface texture and internal quality.

[Brief explanation of drawings]

1 to 3 are explanatory diagrams showing examples of the method of the present invention, and FIG. 4 is a schematic cross-sectional diagram of a slab produced by the method of the present invention.
Figure 5 is an implementation result diagram showing the effects of the method of the present invention, Figures 6-
Fig. 8 is an explanatory diagram of the conventional method, Fig. 9 (a) and (b) are schematic cross-sectional views of slabs manufactured by the strip casting method, Fig. 10 (1 idiot) 15121, Go, 14] Fig. 4 ? Figure 6 Figure 7 Figure 5 Figure 8

Claims (1)

[Claims] (1) In a method of continuously casting thin slabs by cooling and solidifying molten metal from one direction, the molten metal is continuously supplied to a cooling body, and the molten metal is solidified from one direction by the cooling body. 1. A method for continuous casting of a thin plate, characterized by further spraying semi-molten molten metal in the form of droplets onto the non-cooling surface of a slab.