JPH02205236A - Method for continuously casting molten metal - Google Patents

Abstract

PURPOSE:To enable high speed casting and improvement of a cast slab quality by supplying molten powder on molten steel surface in a mold and further, supplying powdery or granular powder on this. CONSTITUTION:Molten steel 5 is poured into the mold 2 through a submerged nozzle 1 from a tundish. Shell 6 developed in the mold 2 is drawn downward and cooled with cooling spray 4 to form a cast slab 7. Then, the molten powder 8a is supplied onto the molten steel surface 5 in the mold 2 from a molten powder supplying nozzle 3. The powdery or granular powder 9a is supplied on this and casting is executed. By this method, lubricating function and heat holding function, which the powder has, can be sufficiently displayed.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to a method for continuous casting of molten metal, specifically a method for continuous casting of molten metal that effectively lubricates the mold during casting and keeps the temperature of the molten metal in the mold. Regarding.

(Conventional Technique WI) In the continuous casting method, mold lubrication during casting and heat retention of the molten metal (hereinafter referred to as molten steel in the case of steel) in the mold are extremely important.

In early continuous casting methods, mold lubrication was performed by oil casting. In this method, as shown in Fig. 1, the molten steel 5 injected into the mold through the immersion nozzle 1 is cooled by the mold 2, and a solidified shell 6 is formed and the gap between the mold and the mold 2 is filled with the mold. Lepseed oil 11 was supplied from an oil supply pipe 10 provided at the top to form an oil film on the inner surface of the mold for lubrication.

However, in this method, when the nonmetallic inclusions contained in the molten steel float to the surface of the molten steel due to the difference in specific gravity while the molten steel 115 circulates within the mold, as shown by the arrow in the figure, There was a problem in that it was trapped in the solidified shell 6 that was generated and deteriorated the surface quality of the slab. Furthermore, this method has the disadvantage that the surface of the molten steel in the mold is directly exposed to the atmosphere, resulting in a significant drop in the temperature of the molten steel and its oxidation.

Therefore, recently, a powder casting method has been used. In this method, as shown in Fig. 2, a powder or granular powder 9a containing calcium oxide, silicon oxide, aluminum oxide, alkaline substances, etc. is supplied in a layer on the surface of molten steel 5, and the lower part is filled with molten steel. The nonmetallic inclusions are melted by heat to form a molten layer 8b, and a powder layer 9b whose upper part remains powdery is formed, and nonmetallic inclusions that separate and float from the molten steel in the lower molten layer 8b. At the same time, the molten powder in the molten layer 8b is allowed to enter between the mold 2 and the solidified shell 6, and the molten powder and the powder solidified layer 8c fixed to the inner surface of the mold perform lubrication, and the upper powder layer 9b Insulates molten steel and prevents oxidation. the result,
Improved lubricity enables high-speed casting, keeps the molten steel warm and prevents oxidation, and significantly improves the surface quality of the slab.

As described above, the use of powder in the continuous casting method has brought about various excellent effects, among which the significance of making high-speed casting possible is extremely significant.

However, in the method of melting the powder or granular powder with the heat of molten steel for lubrication, it is difficult to further increase the casting speed. The problem is that when the casting speed is increased, the amount of molten powder that enters between the mold and the solidified shell decreases, resulting in a thinner film and the risk of breakout (the solidified shell breaks and the molten steel inside the shell flows out). This is because there is.

In order to prevent this breakout, attempts are being made to increase the amount of powder infiltrated by adjusting the physical properties of the molten powder, such as lowering its viscosity, lowering its melting point, and increasing its melting speed. . However, in that case, the powder layer (
There is a problem in that even the powder 9a) shown in FIG. 2 is dissolved, making it impossible to maintain an appropriate layer thickness and sacrificing the heat-insulating effect of the molten steel.

(Problems to be Solved by the Invention) An object of the present invention is to provide a continuous casting method for molten metal that can fully exhibit the two functions of powder, namely, mold lubrication and molten steel heat retention.

(Means for solving the problem) As mentioned above, in the continuous casting method in which powder or granular powder is melted with the heat of molten steel, either the lubrication effect or the heat retention effect must be sacrificed depending on the casting conditions. Something must happen.

Therefore, the inventors of the present invention have conducted various studies on continuous casting methods that can supply powder that is most suitable for the casting conditions without impairing the two functions of the powder. The lower layer is supplied with pre-melted powder that reduces viscosity in a molten state to increase the amount of penetration between the mold and the shell for smooth lubrication, and the upper layer is supplied with powder or granular powder. I learned that if the molten steel is kept warm by using powder, the lubricating and heat retaining functions of the powder can be fully utilized.

This invention was made based on the above findings, and
Its gist is ``a continuous casting method for molten metal in which pre-molten powder is supplied to the surface of the molten steel in the mold, and then powdered or granular powder is supplied on top of that for casting.''

(Function) Hereinafter, the continuous casting method of the present invention will be explained based on the drawings. FIG. 3 is a schematic sectional view of a casting apparatus for carrying out the method of the present invention. In FIG. 0, l is an immersion nozzle, 2 is a mold,
3 is a molten powder supply nozzle, and 4 is a cooling nozzle.

A case in which the casting method of the present invention is carried out using such an apparatus will be described. Molten steel 5 injected from a tundish (not shown) into a mold 2 through a submerged nozzle 1 is cooled by the mold 2 to produce a solidified shell 6. This coagulation seal 6
is pulled downward by pinch rolls (not shown) and cooled by a cooling spray 4 provided under the mold 2, solidifying into a slab 7.

In such a casting process, in the method of the present invention, pre-molten powder 8a is supplied from the molten powder supply nozzle 3 to the surface of the molten steel 5 to form a molten layer 8b.

Powder-like or granular powder 9a is then supplied thereon to form a powder layer 9b.

The powder 8a of the molten layer 8b is mixed with the mold 2 and the solidified shell 6.
It quickly penetrates into the gaps and acts as a lubricant. Further, a part of the powder 8a that has entered is fixed to the inner surface of the mold shown in FIG. 3(b) (an enlarged view of section A in FIG. 3(a)) to form a powder solidified layer 8c. A part of the powder in the powder layer 9b melts and enters the molten layer 8b, but most of the remaining powder remains in the powder layer 9b to maintain a predetermined layer thickness and to keep the molten steel warm and prevent oxidation.

In this way, in the present invention, the lubricating powder and the heat-retaining powder are supplied from separate systems, so that the respective functions can be fully exhibited. Therefore, even in the case of high-speed casting, it is possible to select a powder that matches the casting speed, and since it is melted in advance, physical properties such as viscosity can be adjusted to improve lubricating properties. Moreover, since the melt layer thickness can be freely controlled, breakout can be completely prevented from occurring.

(Example) Continuous casting apparatus as shown in FIG. 3 (immersion nozzle with inner diameter 9mm and 2 holes, molten powder supply nozzle with inner diameter 5a+m, short side 275mm, long side 1600mm+).

It consists of a 900-cm high mold which is injected at 110 cycles/min with a stroke of 7.5 wr- into a low carbon steel melt W4 (in weight percent, C: 0. 05%, Mn: 0.20%, St: 0.0
10%, P: 0.013%, S: 0.004%), and at the same time, molten powder having the melting point and viscosity shown in Table 1 was supplied from the molten powder supply nozzle to the molten steel surface to a thickness of 8IllI. Form a molten layer of
A powder layer was formed. Then, it was drawn at a speed of 2.5 m/min to produce a slab with a thickness of 265 mm and a width of 1572 m+.

The amount of molten powder in this casting was 0.4 kg/ton of molten steel.

Despite the high-speed casting of 2.5 m and 7 minutes, no breakout occurred.

In addition, the thermal insulation powder was hardly consumed and the thermal insulation was good.

As described above, in the present invention, since the supply systems for the powder for lubricating and the powder for heat insulation are separate, the consumption amount can be controlled according to the casting conditions.In the case of this embodiment, the consumption amount of the molten powder could be controlled within the range of 0.28 to 0.60 kg/melt.

As a comparative example, casting was carried out using the conventional method of melting powder powder with the heat of molten steel under the same conditions as above. The powder consumption at this time was 0.27 kg/melt, and the casting speed was 1.8 m.
/ minute was the limit. In the case of this casting, carbon powder was mixed into the powder to adjust its heat retention properties and melting rate, which resulted in an increase in the carbon content of the molten steel.

(Effects of the Invention) As explained above, according to the continuous casting method of the present invention, the lubricating function and heat retaining function of the powder can be fully exhibited. Therefore, high-speed casting becomes possible and it can greatly contribute to improving the quality of slabs.

[Brief explanation of the drawing]

Figure 1 is a diagram illustrating an initial continuous casting method that uses oil for mold lubrication, Figure 2 is a diagram illustrating a conventional continuous casting method that uses powder, and Figure 3 (a) is a diagram illustrating the present invention. Figure 3 (b) is a diagram explaining the continuous casting method using the molten powder and powder powder.
This is an enlarged view of part A in FIG. 3(a). l is an immersion nozzle, 2 is a mold, 3 is a molten powder supply nozzle, 4 is a cooling nozzle, 5 is molten steel, 6 is a solidified shell, 7 is a slab, 8a is a molten powder, 8b is a molten layer, 9a is a powder powder , 9b is a powder layer, 10 is an oil supply pipe, and 11 is oil.

Claims (1)

[Claims] A continuous casting method for molten metal characterized by supplying pre-molten powder to the surface of the molten steel in a mold, and then supplying powder or granular powder on top of the powder to perform casting.