JPH02263542A - Method for continuously casting cast strip composed of single crystal - Google Patents

Abstract

PURPOSE:To easily obtain a striplike wide and long size material composed of single metal crystal by executing cooling to the cast strip so that solidified interface forms single convex face to molten metal. CONSTITUTION:The molten metal 1 is supplied onto surface of a rotating heated mold 3 through a trough 2 to form molten metal bath 4. The molten metal is caused to flow to downstream side according to rotation of the rotating heated mold 3 and cooled with water cooling spray 5, and by cooling of the obtd. cast strip 6, the molten metal is solidified at the solidified interface 7 and the cast strip 6 is continuously drawn with pinch rolls 8. In this case, by making wider the slit width at center part of the cooling water spray nozzle compared with that of both end parts, the solidified interface forms the single convex face and the cast strip composed of the single crystal without any banded structure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a continuous casting method for a band-shaped ingot made of a metal single crystal.

[Conventional technology]

The continuous casting method of strip-shaped ingots using conventional rotary heating molds is as follows:
The surface of the rotary mold, which is the solidification base, is heated above the solidification temperature of the cast metal, and the molten metal is supplied upstream from the top of the rotary mold to form a molten metal bath, and as the mold rotates, the band-shaped molten metal moves with the mold. The ingot produced downstream is solidified by cooling from the upper surface, and a band-shaped ingot having a unidirectionally solidified structure is continuously cast.

The feature of this method is that since a heated mold is used, there is no nucleation or growth of crystals from the mold surface, and the molten metal on the mold surface solidifies only by cooling the ingot itself, so the solidification occurs in a direction parallel to the casting direction. The process progresses to the point where band-shaped ingots consisting of a unidirectionally solidified structure are continuously obtained. Furthermore, by using a wide drum-shaped rotating heating mold, it is possible to easily obtain a band-shaped ingot having a wide unidirectionally solidified structure, which was impossible to obtain in the past.

[Problems to be Solved by the Invention] Generally, it is known that a unidirectionally solidified material produced by a heated mold continuous casting method has better workability than an ingot produced by a cooling mold. However, even if it is a unidirectionally solidified material obtained by continuous casting, as long as there are multiple crystals, there will be segregation of impurities at the grain boundaries, and depending on the processing, problems such as the occurrence of cracks at the grain boundaries may occur. was alive. For this reason, materials without grain boundaries are considered to be of higher quality.
In other words, it has been desired to develop a manufacturing technology for single crystal materials.

Among the continuous casting methods using heated molds, the rotating heated mold type continuous casting method, in which the mold is rotated and the mass is scaled on the surface of the mold into a strip 5 made of unidirectionally solidified weave, is different from the conventional hollow heated Vt type. Compared to the horizontal continuous casting method or the downward continuous casting method, this method has the advantage that there is no risk of breakout of molten metal from the opening end of the mold during casting, and thin-walled strip-shaped ingots can be cast at a faster casting speed. Has characteristics.

However, in the continuous casting method of band-shaped ingots using a rotary mold, as the casting speed increases, a striped structure consisting of a plurality of crystals parallel to the casting direction is formed. This tendency becomes more pronounced as the casting speed increases.

As a result of various studies on the formation mechanism of such a striped structure, it became clear that the formation of a striped structure is caused by the formation of irregularities at the solidification interface due to uneven cooling in the width direction of the band-shaped ingot. Ta.

In other words, when the ingot is cooled using a plurality of water-cooled nozzles arranged in a comb-like line in the width direction of the band-shaped ingot, a striped structure corresponding to the number of water-cooled nozzles is obtained, and the grain boundaries are clearly defined. ,
It was found to extend between each nozzle and parallel to the casting direction.

A band-shaped ingot with multiple crystals extending in the casting direction is
Since there is a risk of cracking at the grain boundaries during processing, there has been a strong desire to develop a method for producing a band-shaped ingot made of single crystal without such grain boundaries.

[Means to solve the problem]

In view of this, and as a result of various studies, the present invention has developed a new technology for continuously manufacturing strip-shaped ingots made of metal single crystals, which was difficult to manufacture using conventional techniques.

That is, the present invention supplies molten metal to the surface of a rotating mold heated above the solidification temperature of the cast metal, cools the surface of the band-shaped ingot produced downstream, and prevents crystal nucleation from the mold surface. By continuously solidifying the molten metal that is in contact with the tip of the ingot, in the continuous casting method for band-shaped ingots with a unidirectional solidification structure, the ingot is solidified so that the solidified interface has no depressions and forms a single six-sided ingot. It is characterized by performing cooling.

An effective means to prevent the formation of concavities that cause segregation lines of impurities and grain boundaries at the solidification interface and to obtain single crystals is to use a cooling device with a single slit-shaped injection port in the width direction of the band-shaped ingot. The lower end of the water curtain, which is formed by jetting from a single slit, is brought into contact with the surface of the strip-shaped ingot. This objective can be achieved by adjusting the shape of the slit opening and the water flow rate so that the width of the slit becomes wider than that of both sides.

Further, when the single slit-shaped injection port has a convex shape, that is, an arcuate shape with respect to the molten metal bath, it is also effective to form a convex solidified surface of the ingot.

[Function] When continuous casting is performed using a rotary heating mold, even if many crystals with arbitrary orientations are formed at the start of casting, their preferential growth directions will become almost aligned, so competitive growth will end and multiple crystals will be formed. grains begin to grow in one direction. As the casting speed increases and the position of the solidification interface approaches the cooling device,
The solidification interface becomes susceptible to the effects of non-uniform cooling, forming irregularities at the solidification interface, causing segregation of impurities in the recesses, and finally leading to the formation of new crystal grain boundaries.

The present invention is a method of preventing the formation of such new grain boundaries and promoting single crystallization through growth competition of crystals nucleated at the solidification start edge.

〔Example] Next, the present invention will be explained by examples.

A case will be described in which a band-shaped ingot made of a single crystal of tin and having a thickness of 31 mm and a width of 50 mm is continuously cast.

FIG. 1 is an explanatory diagram schematically showing a rotary heating mold type continuous casting apparatus used for carrying out the present invention. The molten tin melted in the melting furnace is supplied to the surface of the rotating heating mold through the gutter ■, forming a molten metal bath■. As the rotating heating mold ■ rotates, the molten metal is sent downstream and cooled by the water cooling spray ■.
By cooling the obtained band-shaped ingot (2), the molten metal solidifies at the solidification interface (2), and the band-shaped ingot (2) is continuously pulled out by pinch rolls (2). (2) is a knife for peeling the ingot from the mold. Molten tin heated to 240°C using the first equipment was heated to 235°C in advance, and the width was 50m.
Water is supplied to the top surface of a rotating cast iron foil with a diameter of 5,001 m and has a groove of 31 m in depth, and the water flow line is set as shown in Fig. 2 (Fig. When casting was carried out at a speed of 1000 mm/min by spraying as in (a) above, unevenness was formed at the solidification interface, and a striped structure consisting of 10 rows of crystals was obtained.

When water cooling is performed using a water flow film as shown in Figure 2 (b) using a cooling water spray nozzle consisting of a slit with a width of lllll11, the crystals generated at the solidification start end and aligned by competitive growth grow directly in the casting direction. However, it was not possible to obtain a single crystal.

Next, the width of the slit is 11 m at the center and 0.8 m at both ends.
m, and when the slit in the center is made wider than the slits at both ends, the solidification interface forms a single convex surface as shown in Figure 2 (c), and a band-shaped ingot consisting of a single crystal without a striped structure is formed. Obtained. In addition, the slit with a width of 1 m 1 w is 5 mm in the center compared to both ends.
1. Even when a cooling water spray nozzle curved toward the solidification tip is used, the solidification interface forms a single convex surface, as shown in Figure 2 (d), and a band-shaped ingot consisting of a single crystal without a striped structure is formed. I was able to get it.

〔Effect of the invention〕

As described above, according to the present invention, by heating the mold surface to a temperature higher than the solidification temperature of the cast metal, nucleation of crystals from the mold surface is prevented, and the band-shaped ingot produced downstream is made into a single slab. By using a cooling device to cool the solidification interface so that it becomes convex, it is possible to continuously obtain single-crystal band-shaped ingots without the formation of striped structures, which was not possible with conventional techniques. It has become possible to easily produce long and wide belt-shaped materials made of single crystal metal.
It has remarkable industrial effects.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a continuous casting apparatus for a band-shaped ingot made of single crystal according to an embodiment of the present invention, and FIGS. ) is an explanatory view showing the cross-sectional shape of water flow lines and water film formed by the cooling spray nozzle of the present invention, the shape of the solidification interface of the ingot, and the solidification structure. 1. Molten metal 2. Gutter 31 rotary mold 4. Molten metal bath 5, water cooling spray device 6. Ingot 7. Solidification interface 8, pinch roll 9. Knife 10. Grain boundary 11, water line +2.
running water film

Claims (1)

[Claims] 1. By supplying molten metal to the surface of a heated and solidified base moving in one direction, cooling the surface of the ingot produced downstream, and continuously solidifying the molten metal on the surface of the solidified base, A method of continuously casting a band-shaped ingot consisting of a directionally solidified structure, characterized in that the ingot is cooled so that the solidification interface forms a single convex surface with respect to the molten metal bath. Continuous casting method for ingots. 2. The single crystal according to claim 1, wherein the ingot is cooled by blowing a curtain-like water film or gas film from a single slit-shaped outlet of a cooler provided in the width direction of the upper surface of the band-shaped ingot. Continuous casting method for band-shaped ingots. 3. The continuous casting method for a band-shaped ingot made of a single crystal according to claim 2, wherein the upper surface of the ingot is cooled using a cooling device characterized in that the width of the slit-shaped outlet is wider at the center than at both ends. . 4. The continuous casting method for a band-shaped ingot made of a single crystal according to claim 2, wherein the upper surface of the ingot is cooled using a cooling device characterized in that the slit-shaped outlet is curved convexly toward the molten metal bath. .