JPH0275446A - Method for continuously casting metal round ingot at high velocity - Google Patents

Abstract

PURPOSE:To prevent clogging of a submerged nozzle and to enable stable casting at high speed by arranging taper at upper part of a mold, specifying height of the taper and making the upper end part inner diameter of the taper the specific times of the lower end part inner diameter thereof. CONSTITUTION:The mold 2 having the taper at the upper part of inside shape, cylindrical shape at the lower part thereof and at least >=200mm height of the taper and making the upper end part inner diameter at least 1.2 times of the lower end part inner diameter, is used. Further, a round ingot is drawn so that solidified shell thickness at the neck part 6 of the mold becomes <=3.5mm. By this method, the clogging of the submerged nozzle 1 is not developed, and the stable casting can be executed at high velocity.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for high-speed continuous casting of round slabs.

[Conventional technology]

In continuous casting of round metal slabs, especially round slabs with a small cross section of 200mm-φ or less in diameter, high-speed casting is essential to improve efficiency because the cross-sectional area of the slab is relatively small. Ru.

FIG. 3 is a schematic explanatory diagram of a part of a conventionally used mold and immersion nozzle, in which (a) is a cross-sectional view and (b) is a longitudinal cross-sectional view. In the same figure, (1) is an immersion nozzle, (2
) is the mold, G3) is the molten steel, and the continuous casting powder (4) put into the mold (2) turns into molten slag, forming the mold (2).
and the solidified shell (5) to perform a lubricating action. At this time, if the inner diameter DNI of the immersion nozzle (1) is small, the nozzle is likely to become clogged.
Ca-8i powder has been added to suppress nozzle clogging.

In addition, due to the high discharge speed of the molten steel inlet from the immersion nozzle (1), the scene changes rapidly at the molten steel meniscus, and the powder 4) tends to get caught up in the molten steel (3). is to improve the precision of conventional scene level control,
Alternatively, a method has been adopted in which the viscosity of the powder (4) is increased to reduce the entrainment of the powder into the molten steel.

[Problem to be solved by the invention]

However, even if the above conventional method is used, if the mold ■ has a small inner diameter, for example, if the mold ■ has an inner diameter of 190-■φ,
The outer diameter DNo of the immersion nozzle (1) is 9o, 1φ, and the inner diameter DN
I becomes about 35■■φ, and the nozzle is easily clogged, making the operation unstable. In addition, the distance between the inner surface of the mold (2) and the outer surface of the immersion nozzle (1) is extremely narrow, and therefore, the higher the speed of casting, the wider the scene fluctuations (the more the powder (4) is drawn in, the more the powder (4) is mixed into the mold). 2) and solidified shell ■
Problems such as breakout may occur due to insufficient flow between the casting holes, and the casting speed has been limited to 2.8 to 3.0 m7 for a round slab with a diameter of 187 mm, for example.

It is an object of the present invention to solve the above-mentioned conventional problems and to provide a high-speed casting method for small-diameter round slabs that does not cause clogging of the immersion nozzle, has little scene fluctuation, and allows stable operation.

[Means to solve the problem]

The present inventors have learned from past experience that the inner diameter of the immersed nozzle must be 45 mm or more in order to prevent blockage of the immersed nozzle.
Considering that it is effective to widen the distance between the inner surface of the mold and the outer surface of the immersion nozzle in order to improve powder slag formation, the inner diameter of the mold at the 18 steel meniscus force part was increased (in various directions). As a result of our studies, we have completed the present invention.

That is, the gist of the present invention is to provide a method for continuously casting round metal slabs, in which the inner shape of the mold has a tapered upper part and a cylindrical lower part, and the height of the tapered part is at least 200 fins or more. , use a mold in which the inner diameter of the upper end of the tapered part is smaller than the inner diameter of the lower end (both are 1.2 times larger), and draw out the round slab so that the solidified shell thickness at the mold drawing part is 3.5 mm or less. This is a high-speed continuous casting method for round metal slabs.

[For production]

The present invention will be explained in detail below.

FIG. 1 is a longitudinal cross-sectional view of an example of a mold for carrying out the present invention. Expand to. The reason why the taper is provided is at least 200 mm or more from the upper end of the mold (2) in order to secure the discharge port of the immersion nozzle (1) in the tapered part within 150 fins from the molten steel meniscus. Usually the molten steel meniscus is cast! (2) It is located at a position of about 100 vsm from the upper end, and the immersion nozzle depth is about 1001-.

By using the mold (1) having the above shape, the surface area of the molten steel meniscus becomes larger, the molten metal surface is stabilized, and heat is supplied from the molten steel opening (1) to the powder (4) better.

Figure 2 shows the results of investigating the relationship between the thickness of the solidified shell (■) at the constricted part (6) in the upper part of the mold shown in Figure 1 and the machining strain, where the horizontal axis is the solidified shell thickness and the vertical axis is the machining strain. , In the same figure, the mark 0 indicates a region where cracks do not occur in the slab, the mark * indicates a region where cracks occur, and the mark X indicates a region where deformation resistance is large and the slab cannot be pulled out. From the results shown in the same figure, the mold drawing area (6
) The thickness of the solidified shell must be reduced to 3.5 mm or less or it will not be possible to pull it out. Further, if the processing strain on the slab diameter due to the reduction of the mold inner diameter is 20% or less, no cracks will occur. In order to ensure a solidified shell thickness of 8.51 mm or less, the drawing speed (casting speed If) in this example needs to be 3 ml or more.

〔Example〕

The following will explain based on examples.

Make a mold having the shape shown in Figure 1 above with a radius of 1.0.
19 with a 5m, 4 strand round slab continuous casting machine
A slab with a diameter of 0■■φ was cast, and an investigation was conducted for clogging of the immersion nozzle, changes in the scene, etc. The chemical composition of the test steel is C:
It was cast 10 times in a row from a 1130 ton ladle with α1°5% and Mn: 0.5%. Table 1 shows the shape and inner diameter expansion ratio of the mold, the shape of the immersion nozzle, and the casting speed. For comparison, similar test casting was conducted using the conventional method.

The survey results are also shown in Table 1. In the same table, in the conventional example using a straight mold without a taper, drawing was stopped after 2 hours of casting due to clogging of the immersion nozzle, and in Comparative Example 3, in which a taper was provided at the top of the mold, the expansion rate of the inner diameter of the mold was too large. , the same (in Comparative Example 4, the solidified shell thickness was too thick due to the low casting speed, making it impossible to pull out in both cases. In contrast, in Inventive Examples 1 and 2, the casting speed was high at 3.2 m/min). However, no clogging of the immersion nozzle was observed, there were few changes in the situation, and the operation was in good condition.

(The following is a blank space) [Effects of the Invention] As explained above, when continuously casting round metal slabs, by applying the method of the present invention using a mold with a tapered upper part and an enlarged inner diameter, There is little variation in the scene within the vI mold, there is no clogging of the immersion nozzle, and high-speed and stable casting can be performed.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of an example of # mold for implementing the present invention, Fig. 2 is a diagram showing the relationship between solidified shell thickness and processing strain investigated using the mold shown in Fig. *1, and Fig. 3 1 is a schematic explanatory diagram of a part of a conventionally used mold and immersion nozzle. l... Immersion nozzle 2... Mold 3... Molten steel 4... Powder 5... Solidified shell
6... Mold drawing part name Figure 3 (In (B) Figure 1 IIQ receiving nozzle" / Figure 2 01235"!;

Claims (1)

[Claims] In a method of continuously casting round metal slabs, the inside shape of the mold is tapered at the top and cylindrical at the bottom.
The height of the tapered portion is at least 200 mm or more,
The inner diameter of the upper end of the tapered portion is at least 1.
A mold twice as large is used, and the thickness of the solidified shell at the mold drawing area is 3.
．． A method for high-speed continuous casting of round metal slabs, characterized in that the round slabs are pulled out to a thickness of 5 mm or less.