JPS6132105B2 - - Google Patents

Description

Detailed Description of the Invention In continuous casting, the present invention involves adding molten steel from a subsequent charge onto the last molten steel from a previous charge while it is still in the mold, and continuously casting slabs. Concerning a continuous casting method for drawing.

In this way, the method of connecting and drawing slabs from the front and rear charges is attracting attention as a method that further improves the excellent workability of continuous casting. etc., the molten metal surface of the previous charge in the mold solidifies, and the connection of the slab joining part becomes incomplete, leading to many accidents such as breakage and breakout. Since the subsequent molten steel is poured while the surface of the molten steel from the previous charge is not solidified, the components of the slab near the melting point are mixed, resulting in defects such as cropping of about 1m in front and back after drawing. The economic point remained.

At the applicant's factory, during continuous casting, a steel pipe with a length approximately equal to the width of the slab was placed horizontally on the front charge of the mold so that approximately half of its diameter was submerged below the molten metal surface. However, by pouring molten steel from the subsequent charge onto the molten steel and connecting the steel pipes back and forth in a way that surrounds them, mixing of the components of the slabs before and after the melting area can be avoided, and safe continuous continuous casting has been achieved.
The method of the present invention is different from this, in that the molten steel from the previous charge is positively solidified in the mold, and the molten steel from the subsequent charge is poured onto the slab, thereby making it possible to mix the components. In order to improve the yield by reducing the truncation area near the boundary between adding and adding hot water,
In addition, annular joining jigs are placed at appropriate intervals in the width direction of the slab to form the casting, and this allows the slab from the previous charge and the slab from the subsequent charge to join together to the dummy bar head and the slab. It is characterized in that it is constructed so that it can be connected and pulled out so as to be firmly connected with a tool, so that breakage and breakout accidents caused by pulling out the supplementary continuous cast piece are avoided.

Hereinafter, the method of the present invention will be explained in detail step by step with reference to the drawings.

Stop pouring the molten steel from the previous charge, pull up the immersion nozzle, and evacuate the tundish car from above the mold.

Powder on the surface of the molten metal is removed to the extent that it does not form a skin on the surface of the molten steel (Figure 1 A and B).

A plurality of annular joining jigs 3 are arranged with their ring axes aligned in the width direction of the mold and spaced apart at appropriate intervals so that approximately half of the vertical diameter ld of the rings is submerged below the molten metal surface. Coolant 5 is poured onto the surface to completely solidify the surface (Figure 2, A and B).

The above-mentioned annular joint jig 3 is, for example, an oval shape as shown in FIG. 5, a spectacle shape as shown in FIG.
In the example, considering strength, in the case of a slab with a width of 1800 mm and a thickness of 200 mm, the short axis of the ring is 130 mm, the long axis is 260 mm, and the width is 130 mm.
A set of two oval rings with a wall thickness of 15 to 20 mm were used at intervals in the slab width direction.

Pull out the slab so that the molten metal level in the mold is at an appropriate position (for example, 270 mm below the upper edge of the mold). This is to start additional casting of molten steel in the subsequent charge, but at this time, care must be taken not to cause seal leakage from the bottom of the mold due to lowering the molten metal level too much (Fig. 3 A and B).

The tundish car of the second charge is moved onto the mold, the immersion nozzle 6 is lowered to an appropriate position above the hot water level of the previous charge, and casting is started.

After the start of casting, the slab is held as it is for a while (about 40 seconds), and then drawing is resumed (Fig. 4 A and B).

As described above, the time required from stopping the casting of the previous charge to starting the casting of the next charge and restarting the drawing of the slab is approximately 3 minutes.

According to the method of the present invention, the upper surface of the molten steel of the previous charge is completely solidified before the molten steel of the next charge is poured onto it, so even if the previous charge and the subsequent charge are of different steel types. Also, almost no mixing of steel components occurs.

Figure 7 shows the mixing state of the components near the replenishment boundary for a test slab (3 minutes required for tundish exchange) that was continuously cast by adding a different steel type from the subsequent charge onto the previous charge as described above. In order to investigate this, the analytical values of Mn and Nb at various distances from the melting point are shown in a graph. This was done using chips collected from various distances from the hot water boundary as shown. In the figure, black dots and broken lines are on the side, and white dots and solid lines are on the center side.

Further, according to the method of the present invention, the solidified annular splicing jig is fixed to the upper surface of the molten steel of the previous charge, and the molten steel of the subsequent charge is cast onto it so as to surround the exposed portion of the splicing jig. Therefore, a reliable connection can be obtained between the dummy bar head equipped with a splicing jig and the slab cast on top of the dummy bar head, and there is no risk of accidents such as breakage or breakout when the slab is pulled out. You can work safely without any problems.
With conventional relays, it was necessary to pour the molten steel of the next charge before the top surface of the molten steel of the previous charge had solidified, which caused work delays such as time-consuming opening of the tandate nozzle of the subsequent charge, which caused breakouts, etc. However, with this method, as mentioned above, there is no such risk and work can be continued safely.

Further, as mentioned above, the annular joint jig used in the method of the present invention is for a slab of 1800 mm x 200 mm in width.
It is a small annular piece of steel with a diameter of 130 mm, a minor axis of 130 mm, a major axis of 260 mm, and a wall thickness of 15 to 20 mm.A sufficient safety factor can be obtained by using a pair of these pieces, and the cost is extremely low. Since the vertical diameter in the vertical direction is sufficiently larger than the horizontal diameter, which is subject to thickness restrictions, it is possible to connect the upper and lower slabs with less material and with less material than when using a circular pipe as a joint jig, which is placed horizontally. There are advantages to be gained.

Next, Fig. 8 is a graph showing the state of macroscopic inclusions near the melt boundary of the supplied test slab that was continuously cast using this method. It has been shown that a clean slab can be obtained at certain positions. In this way, the method of the present invention, in addition to the fact that the mixing of components shown in FIG. There is also a remarkable improvement in yield.

[Brief explanation of the drawing]

1 to 4 are explanatory diagrams of the work of the method of the present invention, and in each figure, A is a longitudinal sectional front view, and B is a side view of the same. Fig. 5 shows an example of a circular joint jig, with A being a front view and B being a side view. FIG. 6 is a side view of another example of the annular joint jig. FIG. 7 is a curve diagram showing the analysis test results of components near the replenishment boundary for an example of a continuous slab produced by this method. FIG. 8 is a curve diagram showing the results of an investigation of macroscopic inclusions in the vicinity of the additional hot water boundary. 1: mold wall, 2: molten steel from front charge, 3: splicing jig, ld: same longitudinal diameter, sd: same horizontal diameter, 4: molten steel from after charge, 5: coolant, 6: immersion nozzle.

Claims (1)

[Claims] 1. Temporarily stop pouring from the previous charge tundish, and place multiple elliptical or irregularly shaped joint jigs with the major axis ld vertically and the minor axis sd horizontally on the surface of the mold in the width direction of the mold. Align the ring axes of the splicing jig and place it at appropriate intervals so that approximately half of the major axis ld of the ring is submerged below the molten metal surface, and coolant is poured into the molten metal surface in the mold to cool the surface. A method for continuous continuous casting of steel, characterized by solidifying the steel and restarting the pouring of molten steel from the next charge tundish onto the solidified steel.