JPS6315057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting method for reducing inclusions generated when molten steel is injected into a tundish during continuous casting, and for greatly reducing inclusions in slabs.

In the continuous casting method, molten steel injected from a ladle into a tundish is normally exposed to oxygen in the air, which reacts with Sol, Al, Si, Ti, etc. in the molten steel, producing nonmetallic inclusions. Also, when changing the ladle during continuous casting, etc., the molten steel injection flow from the ladle hits the slag floating in the tundish, and it becomes an inclusion in the continuous slab and has an adverse effect. For this purpose, air oxidation should be prevented as much as possible, and floating slag should be thrown in.
It is important to prevent inclusions and reduce inclusions.

In order to efficiently and economically solve the above-mentioned problems, the present inventors have repeatedly conducted various experiments and studies. Regarding the former, based on the understanding of the actual situation shown in FIG. It was found that this was influenced by the height of the weir installed near the molten steel injection flow contact part in the tundish.

That is, as shown in FIG. 3, H: weir height, h:
When the height is from the bottom of the tundish water contact part to the outlet position of the expansion nozzle 9, the desired purpose is achieved when H-h0, and when H-h<O, air oxidation cannot be prevented and the effect is not achieved. I discovered that.

Regarding the latter, after removing the slag from the next molten steel pouring surface by spraying the slag gas jet from above the molten steel surface or by blowing the slag gas upward from within the molten steel, the ladle injection nozzle When molten steel is injected from the tundish, the molten steel injection flow hits the hot water contact part of the tundish, and then hits the weir to create an upward flow in the opposite direction to the injection flow, and this upward flow causes the slag to be removed from the poured metal surface. We found that exclusion can continue.

The present invention was made based on the above-mentioned knowledge with the aim of reducing the prevention of the formation of molten steel inclusions in the tundish. When pouring into a continuous casting mold, an expansion nozzle that gradually disappears due to the temperature of the molten steel is connected to the lower part of the injection nozzle attached to the bottom of the ladle, and the discharge opening position at the lower end of this expansion nozzle is set in advance so that the molten steel hits the hot water of the tundish injection flow. The ladle is positioned closer to the bottom of the tundish than the height of the weir installed near the weir, and the ladle starts pouring molten steel into the tundish. Then, when the ladle is joined in continuous casting, the injection nozzle of the next ladle is placed above the tundish molten surface. After the slag at the falling position of the molten steel injection stream is removed in advance, injection is started from the injection nozzle of the next ladle.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of a ladle and tundish that implement the present invention, and FIG. 2 is a cross-sectional view taken along the line A-A in FIG.
A plan view of the tundish and weir section in the direction of the arrow, No. 3
The figure is an enlarged sectional view of the main part showing the relationship between the nozzle attached to the bottom of the ladle and the weir when pouring into the ladle starts, and Figure 4 shows the main part just before the start of pouring molten steel into the ladle when joining the ladle in continuous casting. Fig. 5 is an enlarged sectional view of the main part showing the state of the injection flow immediately after the start of pouring molten steel into the ladle during continuous casting of the ladle. 3 is a tundish, 4 is a hot water contact part, 5 is a weir provided near both sides of the hot water contact part 4 at the center of the bottom of the tundish, 6 is a nozzle for flowing out molten steel provided on both sides of the bottom of the tundish, 7 is a The mold, 8 is a slab, and 9 is an expansion nozzle connected to the lower end of the nozzle 2. The nozzle is made of a material that gradually disappears (disappears by melting or burning) when it comes into contact with molten steel at that temperature. The position is closer to the tundish bottom hot water contact part 4 than the height of the weir 5 (the upper end of the weir). 10 is molten steel, 11 is an injection flow, 12 is a waste gas blowing nozzle disposed around the outer periphery of nozzle 2, and 13 is slag on the surface of the tundish hot water.

First, when pouring molten steel from the ladle 1, as shown in FIG. do. At this time, the expansion nozzle 9
The discharge port is immersed in the molten steel before the molten steel 10 crosses the weir 5, and after that, the immersed part gradually disappears, and the non-immersed part remains until the molten metal level rises and reaches the lower end opening of the injection nozzle 2. to completely block air from the injection flow to prevent air oxidation. Also, when connecting cast pots one after another,
Since the expansion nozzle 9 has already melted and disappeared as shown in FIG. 4, the next molten steel injection flow on the tundish surface is removed in advance by a slag removing device, in this example a gas blowing device using a slag gas blowing nozzle 12. After removing the slag 13 at the falling position, injection is started from the nozzle 2, as shown in FIG. At this time, the injected flow 11 once hits the hot water contact part 4 and then hits the weir 5, from which an upward flow is generated, and this upward flow reaches the hot water surface and is divided radially into the molten steel 10 immediately below the discharge port of the nozzle 2. The slag 13 covering the top surface of the is pushed outward. As a result, the slag at the drop position of the injection stream from the nozzle 2 is reliably removed to the outside including its surroundings, and the slag 13 is reliably prevented from being drawn into the molten steel 10 in the tundish by the injection stream 11. .

The shape of the weir 5 is not limited to the one that partitions the tundish in the longitudinal direction as shown in FIG. 2, but can be any shape that forms a frame shape such as a cylinder, bowl, or diamond shape that surrounds the hot water contact area. can be used.

Next, an example of actual operation of the present invention will be explained.

Molten steel (component %, C; 0.05, Mn; 0.30, Si;
0.02, P; 0.01, Al; 0.03, Fe; balance) was tapped into a 340t ladle 1, and poured into the tundish 3 (50t) according to the example shown in Fig. (width 1900 mm) and continuous casting was performed at a drawing speed of 1.30 m/min. However, nozzle 9
The distance h between the position of the discharge port and the bottom of the hot water contact part 4 is
200mm, height H of weir 500mm, distance between weirs 5 and 5.
900mm, tundish water level height maintenance level l
1500 mm, and then add 2 molten steel with the same composition as the front pot.
I cast a charge one after another. At this time, the pot joints of each charge were performed using the method shown in FIGS. 4 and 5, respectively.

However, the height level l of the tundish hot water at the time of starting injection from the nozzle 2 during pot joining of each charge was 1000 mm, and the distance between the nozzle 2 outlet and the hot water level was 30 mm.

The results of measuring the inclusions in the slab in accordance with the length of the slab are shown in FIG. 7 in comparison with the conventional example. As is clear from Fig. 7, the method according to the present invention can significantly reduce the number of inclusions compared to the conventional example, and also reduce the dispersion thereof, making it possible to obtain high-quality slabs with extremely high cleanliness. .

In the conventional method shown in FIG. 7, casting is performed without using the weir 5, nozzle 9, and waste gas blowing nozzle 12 shown in FIGS. 3 to 5 at all, and the other conditions are the same as those according to the present invention. It is.

As described above, according to the method of the present invention, molten steel is prevented from being oxidized in the air at the initial stage of continuous casting, and slag floating on the top surface of the molten steel at the starting position of molten steel injection in the tundish during pot jointing can be removed with good workability, economy, and efficiency. It is possible to substantially completely prevent slag from being hammered in and engulfed by the injection flow, greatly reducing the number of inclusions in the tundish, and greatly reducing the amount of inclusions in the mold and slab. The effects that can be obtained are extremely large, such as being able to stably produce high-quality slabs with a high yield.

[Brief explanation of the drawing]

In the accompanying drawings, Fig. 1 is an explanatory diagram of an embodiment of the present invention, and is a cross-sectional view mainly showing the ladle and tundish, and Fig. 2 is a view along arrow A-A in Fig. 1, showing a plane of the tundish and weir. Figure 3 is an enlarged sectional view of the main part showing the relationship between the nozzle attached to the bottom of the ladle and the weir,
FIG. 4 is an enlarged cross-sectional view of the main part showing the state immediately before the start of injection during continuous pot joining, and FIG. 5 is an enlarged cross-sectional view of the main part showing the state of the molten steel flow immediately after the start of injection during continuous casting, FIG. 6 is a graph showing the experimental results that are the premise of the present invention, and FIG. 7 is a graph showing the inclusion index in the slab when the casting method of the present invention is used in comparison with the conventional example. In the figure, 1... ladle, 2... nozzle, 3... tundish, 4... hot water contact part, 5... weir, 6...
Pouring nozzle, 7...Mold, 8...Slab, 9...
Expansion nozzle, 10... Molten steel, 11... Injection flow, 1
2...Slag gas blowing nozzle, 13...Slag.

Claims (1)

[Claims] 1. When pouring the molten steel in the ladle into the continuous casting mold through the tundish, an expansion nozzle that gradually disappears at the temperature of the molten steel is connected to the lower part of the injection nozzle attached to the bottom of the ladle, and a discharge port at the lower end of this expansion nozzle. The position is set in advance to be closer to the bottom of the hot water contact than the height of the weir provided near the hot water contact for the molten steel injection flow of the tundish, and then the injection of molten steel from the ladle to the tundish is started, and then when the ladle is joined for continuous casting,
A method for pouring molten steel into a tundish in continuous casting, characterized by starting injection from the pouring nozzle of the next ladle after previously removing slag at the position where the molten steel pouring stream falls from the pouring nozzle of the next ladle onto the surface of the tundish.