JPS591055A - Method for starting charging of molten steel without oxidation to continuous casting tundish - Google Patents

Abstract

PURPOSE:To stabilize the quality of a continuous casting product and to improve yield by preventing the oxidation of the molten steel to be charged into a tundish in an inert gaseous atmosphere, and covering the surface of the molten steel with the melt of a refractory board floating on the surface of the molten steel thereby preventing the oxidation of the molten steel. CONSTITUTION:A board 12 of a refractory material is provided so as to segment a tundish 1 to two upper and lower chambers, and after the tundish 1 is preheated, an aperture 14 for distributing flame is closed with a cover 16 of a refractory board, and an inert gas is blown from an inert gas suction pipe 6 into the space under the board 12. The charging of molten steel into the tundish is started from a long nozzle 8 of a ladle, and when the surface of the charged molten metal rises up to the board 12, the blowing of the inert gas is stopped; at the same instant, the board 12 is melted by the heat of the molten steel so as to cover the surface of the molten steel, whereby the method for starting charging of the molten metal without oxidation into the continuous casting tundish is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing oxidation of molten steel at the start of injection of molten steel into a tundish of a continuous casting apparatus.

When pouring molten steel from the ladle into the tundish, a ladle long nozzle is used to prevent the molten steel from being oxidized by the atmosphere, and its tip is immersed in the molten steel in the tundish to block the molten steel from the atmosphere and prevent its oxidation. However, at the start of pouring molten steel from the ladle into the tundish, the molten steel is exposed to the atmosphere until the tip of the ladle long nozzle is immersed in the molten steel in the tundish, resulting in significant oxidation of the molten steel. .

If the oxidation products associated with molten steel oxidation at the start of pouring molten steel from the ladle into the tundish are captured in the steel, they become non-metallic inclusions that deteriorate the quality of the steel and cause defective products. Tomo, Naru.

Reducing non-metallic inclusions at the start of pouring molten steel from a ladle into a menditsch is an important issue, and various oxidation prevention methods have been proposed.

FIG. 1 shows an example of a conventional method, and is a partial vertical sectional view of a tundish. 1 is a tundish, and 4 is a mendish lid, in which a molten steel injection hole (long nozzle insertion hole) 2, preheating burners if, s, etc. are opened. 3 is a Menditsch nozzle hole. Prior to the start of molten steel injection, the tundish is heated with a preheating burner, and then an inert gas is blown into the tundish from the top of the tundish through an inert gas blowing pipe 6 to create an inert gas atmosphere inside the tundish.

In this method, it is difficult to create an inert gas atmosphere inside the tundish for the following reasons.

(1) There are many openings in the tanditshu lid.

(2) It is difficult to seal between the mendish and the tandish lid.

(3) A large amount of gas is required to replace the entire internal volume of the tundish with inert gas, which is difficult to complete in a short period of time. In order to complete the replacement in a short time, it is necessary to have equipment that can inject a large amount.

Next, FIG. 2 shows an example of another conventional method, and is a partial longitudinal sectional view of a tundish. 1 is Tanditshu, 3
is the menditshu nozzle hole, 4 is the tanditshu lid, 8
9 is a ladle long nozzle, 9 is a splash can, and 6 is an inert gas blowing pipe.

An iron splash can 9 is placed at the tip of the ladle 8.
This method attempts to prevent re-oxidation of the molten steel by setting an inert gas atmosphere inside the streaky can and starting injection of molten steel through the ladle long nozzle 8.

Although this method makes it easy to create an inert gas atmosphere inside the splash can 9, it is not possible to prevent oxidation of the molten steel after the two cans of tin and one can 9 have been melted.

The object of the present invention is to provide a method for starting injection of molten steel without oxidation, which eliminates such conventional drawbacks.

The present invention will be described in detail below with reference to the drawings.

FIGS. 3(a) and 3(b) are a partial vertical cross-sectional view of a tundish illustrating an embodiment of the method of the present invention and a view taken along the line A-A of the same.

In FIG. 3, 1 is a tundish, 4 is a tundish lid, 5 is a preheating burner hole, and 8 is a ladle long nozzle.

In the method of the invention, a refractory board 12 is used.

The refractory board 12 is formed by molding a tundish hot water surface coating material using a binder, and is a plate-shaped body that divides the interior of the tundish 1 into two upper and lower chambers, as shown in FIG. The lower refractory bow 12 has a preheating flame distribution opening 14 for distributing the preheating flame to the two compartmented chambers, and this opening 1.
4, a hole 18 for blowing inert gas, and a hole 19 for a ladle long nozzle. In the example shown in FIG. 3, the refractory board 12 is divided at the ladle long nozzle opening 19, but it can be divided into any number of suitable sizes for ease of handling. can.

The present invention includes: (1) The refractory board 12 is arranged so as to divide the tundish 1 into two upper and lower chambers, and after preheating the inside of the tundish 1, the flame distribution opening 14 is closed with the refractory board lid 16. Step (2) Inert gas is blown into the space under the refractory board 12 through the inert gas blowing pipe 6. Step (3) Injection of molten steel is started through the ladle long nozzle 8, and the molten steel is injected. After the surface reaches the refractory board 12, the inert girth injection is stopped and the refractory board is melted by the heat of the molten steel to cover the surface of the molten steel. This is a method for starting injection of molten steel into a cast tundish without oxidation.

The refractory board 12 divides the inside of the tundish 1 into two upper and lower chambers, and divides the tundish preheating flame into the upper and lower two chambers at an appropriate ratio 5, for example, a flame ratio of 30% in the upper chamber and 70% in the lower chamber, to achieve a good sewing rate. The function is to perform preheating, and to form a small volume of inert gas replacement area in the lower part of the tundish.After the hot water level in the tundish rises, it floats on top of the hot water surface and covers the hot water surface, minimizing the bare hot water surface area as much as possible. It has the function of narrowing and preventing oxidation of the molten steel, and the function of finally melting with the heat of the molten steel and becoming a molten metal surface coating agent.

The material of the refractory board 12 is equivalent to a mendicinal coating powder that covers the surface of the molten steel poured into the tundish 1 and shields it from the atmosphere, such as Sing, '40.
4%, CaO; 35.3%, 1zoa; 7.8-
The main component is de-12, which has a softening point of about 1210°C.
shall be. As the binder, an organic binder such as a phenol resin, a furan resin, an amino resin, a tar pitch, an epoxy resin, a urea resin, or an inorganic binder such as aluminum phosphate can be used depending on the case.

The refractory board 12 has flame distribution holes 14 so that the flame can sufficiently preheat the lower part of the tundish when the inside of the tundish 1 is preheated by a burner. The periphery 15 of the flame distribution opening 14 is preferably made of a material that does not dissolve even when exposed to the burner flame, such as magnasia aggregate, which is hardened with the binder described above.

After the preheating is completed, the flame distribution holes 14 are inserted into the refractory board lid 1.
6 to close. The refractory board lid 16 may be made of the same material as the refractory board 12, but the portion 17 exposed to the preheating burner flame is made of a material that will not be melted by the burner flame.

In Fig. 3, the lid 16 is placed adjacent to the opening 14 for convenient closure, but if the lid 16 is placed in a place that is not exposed to the preheating burner flame and preheated, the entire lid 16 will melt after coming into contact with molten steel. It can be made of uniform material.

In addition, in FIG. 3(,), the state of the refractory board lid 16 when the lid is closed is shown by a broken line 16a.

In the first step of the present invention, the refractory board 12 is arranged in the mendish 1 so as to divide the tundish 1 into two upper and lower chambers, and after preheating the inside of the tundish 1, the flame distribution opening 14't-refractory This is the step of forming a space under the refractory board, which is closed with a refractory board lid 16 and into which inert gas is blown.

This step is carried out in tanditush preheated water.

First, the refractory board 12 is placed and supported on a refractory bracket 13 protruding from the inner surface of the side wall of the tundish 1. This supporting means may include other means capable of mounting the refractory board 12 in a fixed position and floating it on the upper surface of the molten steel when the upper surface of the molten steel rises, such as suspending the refractory board 12 from above using a wire or the like. Any appropriate means can be used.

The refractory boat 12 is preferably located as low as possible within the tundish 1.

Next, the Mendish lid 4 is set.

Next, the refractory inside the tandish 1 is preheated to raise the temperature of the inner surface of the refractory to 1,000 to 1,200°C, and when the molten steel is injected into the tandish, the temperature of the molten steel is prevented from dropping rapidly, and the refractory is Prevent cracking, etc.

Preheating of the inside of the tundish is carried out by burning the burner (after setting the preheating nozzle so that it faces inside the tundish) through the preheating burner opening 5 opened in the mendish lid 4. Thus, 1 tanditsh, 1 refractory board.
2. Raise the temperature of the refractory board lid 16j.

After the temperature rise is completed, the combustion of the burner is stopped, the burner is removed, and the flame distribution opening 14 of the refractory board 12 is closed with the refractory board lid 16, completing the formation of the inert gas injection space.

After completing the preheating stage, the tandyer 3-1 moves to the continuous casting strand injection position, and the first stage ends.

The second step of the present invention is the step of blowing inert gas into the space under the refractory board through the inert gas blowing pipe 6.

After the continuous casting strand has been moved to the injection position, the inert gas blowing pipe 6 is set on the tundish 1, inert gas is blown in, and the ladle 10 containing molten steel is mounted on the tundish.

The inert gas blowing pipe 6 passes through the openings 7 and C18 provided in the tundish lid 4 and the refractory board 12, respectively, so that its tip faces the space below the tundish below the refractory board 12, and is filled with arbon gas, etc. of inert gas is introduced.

On the other hand, a ladle 10 containing molten steel is set above the mendish 1, the ladle long nozzle 8 is suspended through the injection port 2 provided in the mendish lid 4, and the refractory board 1
No. 2 ladle long nozzle [passes through the R hole 19 and is stopped at a predetermined position facing the tundish bottom protrusion 11o.

When the atmosphere under the tundish under the refractory board is replaced with an inert gas atmosphere by introducing an inert gas through the inert gas blowing pipe 6, the second stage is completed, and the process moves on to the third stage of molten steel injection work.

In addition, in the second stage, the sliding nozzle 21 of the ladle 10 and the sliding nozzle 2 of the mendicue 1
It goes without saying that 3 should be closed.

Next, in the third step of the present invention, injection of molten steel is started through the ladle long nozzle 8, and the surface of the molten steel injected reaches the refractory board 12.
After reaching this point, the inert gas injection is stopped and the refractory board 12 is melted by the heat of the molten steel to cover the surface of the molten steel.

While blowing inert gas into the space under the refractory board 12 of the mendices 1, slide the sliding nozzle 2 of the ladle 1o.
1 to open the cylinder 22, and the injection of molten steel from the ladle long nozzle 8 to the bottom of the refractory board 12 is started. Inert gas is continued to be blown in until the level of the molten steel injected into the tundish 1 rises and reaches the refractory board 12, and the molten steel is poured while preventing oxidation.

The tip of the ladle long nozzle 8 is immersed in the molten steel, and when the molten metal surface reaches the refractory board 12, the refractory board 12 floats above the molten metal surface. When this state is reached, stop blowing inert gas.

In this way, the molten steel at the start of injection into the mendices is reliably injected in an inert gas atmosphere and oxidation is prevented.

Most of the #1 part of the refractory board 12 floating on the surface of the molten metal melts due to the heat of the molten steel, and acts in the same way as a normal tundish surface coating, minimizing oxidation of the molten steel. Can be suppressed.

It is also possible to replenish the surface of the hot water with a regular tanditsu hot water surface coating agent.

After the level of the hot water in the water supply 1 reaches a predetermined level, the cylinder 24 is activated.
and begin pouring molten steel into the mold.

Since the present invention is configured as described above, non-oxidizing injection can be performed at the start of pouring molten steel into the continuous casting tundish, and the quality of continuous casting products can be stabilized and the yield can be improved.

FIG. 4 is a graph illustrating the excellent effects of the present invention. This is a graph drawn by taking the slab casting length as - and 9 on the horizontal axis and the change in oxidation amount on the vertical axis, that is, the difference between the amount of oxygen in the slab and the amount of oxygen in the ladle medium temperature steel, and 31 in the figure. 1, 32 is the method shown in FIG. 2, and 33 is the method shown in FIG. 3. From FIG. 4, it can be seen that the method of the present invention has a remarkable effect on the slab quality at the start of casting.

[Brief explanation of drawings]

1 and 2 are partial longitudinal cross-sectional views of a menditsch showing a conventional method, and FIG. 3 shows an embodiment of the present invention, in which (a) is a partial longitudinal cross-sectional view of a menditsh (B-B in FIG. Arrow view)
, (b) is a view taken along the line A-A in FIG. 4, and FIG. 4 is a graph showing changes in the amount of oxidation of the slab. 1...Tandish 2... Molten steel injection hole (ladle long nozzle insertion hole)
3...Tandish nozzle hole 4...
・Tandish lid, 5...Preheating burner hole 6・
...Inert gas blowing pipe 7...Inert gas blowing hole 8...Ladle long nozzle 9...Splash can, 1o...Ladle 1
DESCRIPTION OF SYMBOLS 1... Tandish bottom convex part 12... Refractory board, 13-... Bracket 14... Preheating flame distribution opening 15... Preheating flame distribution opening periphery 16... Refractory board Lid 16a...Closed state of refractory board lid 17...Flame contact portion 113 of refractory board lid...Aperture for inert gas injection 19...Aperture for ladle long nozzle 21. ... Ladle sliding nozzle 22 ... Cylinder 23 ... Tanditshu sliding nozzle 24
...Cylinder 31, 32, 33...Fig. 1, Fig. 2, Fig. 3 respectively
Amount of oxidation according to the method shown in the figure.

Claims (1)

[Scope of Claims] A refractory board made of a hot water surface coating material and having holes for preheating flame distribution, holes for inert gas blowing, and holes for a ladle long nozzle. is arranged in the mendices so as to be divided into two upper and lower chambers, and after preheating the interior of the mendices, closing the preheating flame distribution openings with a lid; Blow gas into the space under the refractory board, start pouring molten steel into the tundish through a ladle long nozzle, and after the surface of the poured molten steel reaches the refractory board, A method for starting non-oxidized injection of molten steel into a continuous casting tundish, comprising the steps of stopping the injection of active gas and melting the refractory board with the heat of the molten steel to cover the surface of the molten steel.