JPS60244453A - Removal of inclusion in molten steel - Google Patents

Abstract

PURPOSE:To float and remove the inclusions in a molten steel by providing a refractory cylindrical body having an inflow port for the molten steel to the upper part of the nozzle aperture in the bottom of a tundish, supplying an inert gas to the inside of the cylindrical body and stirring the molten steel by a rotor. CONSTITUTION:The refractory cylindrical body 3 is installed above the aperture of the immersion nozzle 6 provided in the bottom of the tundish 2. The molten steel 14 poured from a ladle 1 into the tundish flows through the inflow port 12 provided to the body 3 into the body 3 in the direction tangential to the inside surface thereof and rotates the rotor 5 provided in the central part in the direction opposite from the inflow direction of the molten steel. The inert gas such as Ar is at the same time supplied in the state of foam 15 to the molten steel in the body 3 through a nozzle 7. The large inclusions in the molten steel are gathered to the central part by the centrifugal force generated by the rotation of the rotor 5 and are floated on a molten slag surface 13. The small inclusions are adsorbed to the inert gaseous foam fined by the rotor 5 in the mid-way of descending together with the downward flow of the molten steel 14 by which said inclusions are floated together with the foam 15 on the surface 13 and are thereby removed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for removing inclusions in continuous casting of molten steel.

(Prior Art) Inclusions in steel materials cause quality defects, and various measures have been taken to remove or reduce them.

During continuous casting of molten steel, the molten steel is poured into a mold via a tundish (intermediate container). In order to separate and remove inclusions from molten steel, a method is already known in which a weir is provided in the tundish to adjust the flow of the molten steel to be as straight as possible so that the inclusions tend to float naturally.

Although this method separates and removes a considerable amount of inclusions within the tundish, it does not reach the level where there is no problem with the quality of the steel material. Separation of inclusions.

This is because unless the removal ability is sufficient, molten steel containing large inclusions may be sent into the mold.

In addition, small inclusions (about 100 μm or less) that are difficult to float according to the so-called Stokes' law enlarge and grow in the injection nozzle or mold, becoming harmful to a size of 100 μm or more, which forms a solidified layer in the mold. There is also a risk that it may be captured.

As a method for removing inclusions, for metals with low melting points such as aluminum whose production volumes are relatively small, a method of separating inclusions using a solid filter (for example, one made of alumina) is used. However, it is difficult to find suitable solid filter materials for materials such as steel, which have high melting points and are produced in large quantities. If a filter made of a refractory material with weak strength is used, the damaged filter material itself may become a source of inclusions.

If fine inert gas bubbles are injected into molten metal to create a region with a high density of fine bubbles, inclusions collide with the bubbles while the molten steel passes through the region, reducing the overall specific gravity and reducing the amount of inclusions. It is thought that the floating separation of objects is significantly promoted.

As described above, as a method of separating and removing inclusions in molten metal using inert gas bubbles, a method in which gas is blown into the porous bricks or panels attached to the bottom or side of the tundish is particularly popular. It is disclosed in Japanese Patent Publication No. 53-89828. However, in this method, since the bubbles are separated only after they have grown considerably, the bubble diameter is large, and the dispersion range of the bubbles is small, so that a sufficient inclusion removal effect cannot be obtained.

Inside the tongue tissue, a rotor is immersed above the nozzle for injecting molten steel into the mold and rotated.
Japanese Patent Application Laid-Open No. 134508/1983 discloses an inclusion removing means that makes inert gas bubbles blown into molten steel finer.

In this method, inert gas bubbles blown into molten steel are made fine and a weak upward flow is formed as the bubbles rise due to their buoyancy. However, in such inclusion removal means, the molten steel containing inclusions flows laterally into the part where the density of inert gas bubbles is small between the rotor and the nozzle that causes the molten steel to flow out from the tundish. Inclusions cannot be removed.

In addition, the refinement of inert gas bubbles injected into molten steel
The problem tends to be accelerated as the relative speed difference between the molten steel flow and the rotor increases, but as the rotation speed of the rotor increases, vortices are generated on the molten steel surface, causing floating inclusions to be re-engulfed. was there.

(Object of the Invention) The present invention has been made with the object of providing an inclusion removal method that solves the problems in the prior art described above.

(Structure of the Invention) The gist of the present invention is to dispose a cylinder having a molten steel inflow hole on its peripheral wall at a position where a molten steel injection nozzle exists inside a tundish used for continuous casting of molten steel, and to The inert gas is supplied from the inflow hole and blown into the cylindrical self-molten steel, and the inert gas blown into the cylindrical molten steel is further atomized by a rotor that is immersed in the cylindrical molten steel and rotated. A method for removing inclusions in molten steel, characterized in that a cylinder having a molten steel inflow hole on its peripheral wall is disposed at a position of a molten steel injection nozzle inside a tundish used for continuous casting of molten steel; An inner cylinder whose opening lower end is located below the inflow hole is provided, molten steel is supplied from the inflow hole, an inert gas is blown into the molten steel in the cylinder, and the molten steel is further immersed in the molten steel in the cylinder. By the rotor that is rotated,
A method for removing inclusions in molten steel, characterized in that the inert gas blown into the molten steel in the cylinder is atomized, and
In each of these methods, inert gas is injected from an immersed tuyere or porous plug provided in the kundish, or from a porous type tuyere, an immersed lance in a cylinder, or a porous plug provided either on the rotor or on the peripheral wall of the cylinder. This is the way it is done.

The configuration of the present invention will be explained in detail below using illustrated examples.

FIG. 1 shows one embodiment of an apparatus for carrying out the invention.

In FIG. 1, a ladle 1 receives and conveys molten steel refined in a steelmaking furnace such as a converter, and supplies the molten steel to a tundish 2 from a nozzle provided on its lower surface. A cylindrical cylinder 3 is made of refractory material and is disposed above a molten steel injection nozzle 6 provided on the bottom of the tundish 2. The cylinder 3 is fixed to the bottom of the tundish 2, or its upper surface is fixed to a supporting device 8, which will be described later, so that it can be attached and detached. The cylinder 3 has a molten steel inflow hole 12 on its peripheral wall surface.
is drilled tangentially.

The number and shape of the 120 molten steel inflow holes are not particularly limited and should be determined depending on the amount of molten steel that should pass through the cylinder 3, but the molten steel inflow holes 12 should be arranged along the tangent line of the cylinder as shown in FIG. It is preferable to drill in the axial direction and at an axial position near the slug 13.

This increases the chance of contact between the bubbles 15 in the molten steel in the cylinder 3 and the molten steel flow, and improves the inclusion removal rate.

Further, the inflowing molten steel flow from the molten steel inflow hole 12 becomes a swirling flow along the inner wall surface of the cylinder 3 by providing the molten steel inflow hole 12 in the tangential direction on the peripheral wall surface of the cylinder 3.
A high contact speed between the molten steel flow and the rotor 5 can be obtained by making the direction of rotation of the rotor 5 opposite to the direction of the swirling flow.

The inner cylinder 4 is made of refractory material like the cylinder 3, and has an axial length such that the lower end of the opening faces a position below the molten steel inflow hole 12 of the cylinder 3, and the rotor 5, which will be described later, It has an outer diameter smaller than the inner diameter of the cylinder 3 so as to surround the rotation axis of the cylinder 3.

A rotor 5 is made of metal, and the parts exposed to molten steel and high temperatures are protected by refractories, and is positioned within the cylinder 3 by a support device 8 that can move up and down and rotate. Rotor 5
is rotationally driven by a motor 9 through a shaft 10° gear 11.

The planar shape of the rotor 5 is symmetrical with respect to the rotation axis, and has a stepped groove surface extending in the axial direction as shown in FIGS. 3(a) and 3(b) on its outer peripheral surface. It is desirable that the shape and number of the grooves on the circumferential surface of the rotor 50 are determined based on the number of rotations of the rotor 50, the amount of blown gas, and the amount of molten steel passing through.

In this embodiment, the inner cylinder 4 has its upper surface fixed to a support device 8 for the rotor 5. The inner cylinder 4 receives molten steel from the molten steel inflow hole 12 of the cylinder 3 when air bubbles containing inclusions gather on the rotor 5 side and float due to the centrifugal effect due to the swirling flow of the molten steel from the molten steel inflow hole 12 of the cylinder 3. It functions to prevent air bubbles from being trapped in the molten steel and to prevent floating inclusions from being drawn into the molten steel.

7 is an inert gas supply pipe, which injects bubbles 15 of an inert gas such as Ar gas into the molten steel in the cylinder 3 through a molten steel injection nozzle 6 made of porous bricks. supply

In the embodiment shown in FIG. 1, the inert gas such as Ar is supplied from the supply pipe 7 through the porous brick constituting the molten steel injection nozzle 6. In this case, the tundish may be provided with porous type immersion tuyeres, and the inert gas may be supplied into the cylinder 3 from the immersion tuyeres.

Alternatively, an immersion lance may be provided in the cylinder 3 and the inert gas may be supplied from there, or porous bricks may be buried in the bottom of the rotor 5 and the inert gas may be supplied through the inside of the rotating shaft 1o. It's okay.

Furthermore, a porous brick may be embedded in the inner circumferential wall of the cylinder through the inside of the wall of the cylinder 3, and the inert gas may be supplied into the cylinder 3 from there.

(Operation) An embodiment of the present invention will be described using the apparatus configured as described above.

The molten steel 14 supplied from the ladle 1 to the tundish 2 is
The inclusions reach the cylinder 3 while being floated and separated, and flow into the cylinder 3 as a swirling flow through the molten steel inflow hole 12 formed in the cylinder 3.

Inside the cylinder 3, Ar is supplied from an inert gas supply pipe 7.
Gas is supplied as bubbles 15 through the porous bricks 6.

After the Ar gas bubbles 15 in the molten steel inside the cylinder 3 expand in volume due to the heat from the molten steel, they come into contact with the stepped grooves formed in the rotor 5, which rotates in the opposite direction to the swirling flow of the molten steel inside the cylinder 3, and become fine. be done. The fine Ar gas bubbles float between the rotor 5 and the cylinder 3.

Among the inclusions that ride the molten steel flow and enter the cylinder 3 from the molten steel inflow hole 12, large inclusions gather at the center of the cylinder due to centrifugal force, and are floated and separated by the floating flow existing in the center and the floating side of Stokes. Ru.

Small inclusions ride the flow and descend inside the cylinder 3, and the rotor 5
It passes between the rotating shaft 10 of the cylinder 3 and the inner wall surface of the cylinder 3. At this stage, the inclusions are adsorbed by the finely divided inert gas bubbles and are floated and separated together with the bubbles.

(Example) Using the apparatus shown in Fig. 1, low carbon aluminum killed steel (0
: 0.05 wz%, At: 0.0 1 to 0.0 3
wt%) was continuously cast.

The molten steel in the ladle was 250 tons, and the molten metal in the tundish was continuously cast for 301.6 heats in a steady state.

The tandish was lined with magnesia, and a slab (cross section 1300m wide x 15°3 thick) was cast with two strands. The average casting speed is 3,6 t/strand
min, the injection molten steel temperature is 1550-1570°C. The diameter of the injection nozzle (parallel part) is 5°.

U of thin plate products obtained under each injection condition shown in Table 1
The ST defect occurrence rate is divided into the joint part (at the start of pouring, at the time of ladle replacement, at the pouring path, etc., corresponding to about 10% of the total slab) and the steady part, and is shown in Table 2. show.

Table 1: Manufacturing conditions: Table 2: Number of defects detected by ultrasonic testing on finished products (K/1 o O
m') In the conventional method, both the joint and steady parts were defective,
It can be seen that according to the method of this invention, the number of defects is reduced to zero, and the effect of adsorption and separation of inclusions is increased.

(Effects of the Invention) Since the present invention is configured and operated as described above, the molten steel supplied to the tundish is made to pass through a region with high bubble density before being injected into the mold. Therefore, inclusions can be sufficiently adsorbed and removed. When an inner cylinder is used, air bubbles containing inclusions float inside the inner cylinder, so slag re-entrainment is reduced.

In addition, the surface of the slag is insulated by the floating argon,
It has great effects, such as eliminating the need to worry about slag oxidation.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the apparatus used when carrying out the present invention, FIG. 2 is a diagram showing an example of the direction and position of the molten steel inlet hole 12 bored in the cylinder 3, and FIG. 3A and 3B are diagrams showing an example of the shape of a stepped groove formed on the outer circumferential surface of the rotor 5, with FIG. 3(a) being a side view and FIG. 3(b) being a plan view. l...Ladle, 2...Tandish, 3...Cylinder, 4
...Inner cylinder, 5.Rotor, 6. Molten steel injection nozzle,
7... Inert gas supply pipe, 8... Support device, 9...
Motor, 10, shaft, 11, gear, 12, molten steel inflow hole,
13. Slag, 14. Molten steel, 15. Inert gas bubbles. Agent: Patent Attorney Masamitsu Akizawa and 2 others d -Q Spontaneous procedure amendment dated June 1980, Director General of the Patent Office], Indication of case: Japanese Patent Application No. 1982-1.00162 No. 2, Title of the invention Method for removing inclusions in molten steel 3, relationship with the case of the person making the amendment Application Address 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name Secret 6
6G) Nippon Steel Corporation 4, Agent address: 12-1-5 Nihonbashi, Chuo-ku, Tokyo Number of inventions increased by the amendment None Contents of the amendment (1) Page 9 of the specification, line 4 and TX 5 of the same ``Swirling flow'' in the line is changed to ``Swirling flow''.

Claims (6)

[Claims] (1) A cylinder having a molten steel inflow hole on its peripheral wall is provided at the position of the molten steel injection nozzle inside the tundish used for continuous casting of molten steel, and molten steel is supplied from the inflow hole, and the molten steel in the cylinder is Inclusions in molten steel characterized in that an inert gas is blown into the molten steel, and the inert gas blown into the molten steel in the cylinder is made fine by a rotor that is immersed in the molten steel in the cylinder and rotated. Removal method. (2) The method for removing inclusions according to claim 1, wherein the inert gas is blown into the molten steel in the cylinder through an immersion tuyere, a porous plug, or a porous type tuyere provided in a tundish. (3) Claim 1, in which the inert gas is injected into the molten steel in the cylinder through a cylindrical immersion lance or a porous plug provided on either the rotor or the cylindrical peripheral wall surface.
Inclusion removal method described in section. (4) A cylinder having a molten steel inflow hole on its peripheral wall is disposed at the position of the molten steel injection nozzle inside the tundish used for continuous casting of molten steel, and the lower end of the opening is located within the cylinder below the inflow hole. The molten steel is supplied from the inflow hole, an inert gas is blown into the molten steel in the cylinder, and a rotor is immersed in the molten steel in the cylinder and rotated. A method for removing inclusions in molten steel, characterized by atomizing an inert gas blown into the molten steel. (5) The inclusion according to claim 4, wherein the inert gas is blown into the molten steel in the cylinder through an immersed tuyere, a porous sprag, or a porous type tuyere provided in the tundish. Removal method. (6) The intervention according to claim 4, wherein the inert gas is blown into the molten steel in the cylinder through a porous plug installed in either the immersion lance in the cylinder, the rotor, or the peripheral wall of the cylinder. How to remove objects.