JPS59110421A - Removing method of inclusion - Google Patents

Abstract

PURPOSE:To remove efficiently an inclusion in a molten steel by a method having a high practical use by injecting the molten steel into a casting mold through a filter mechanism consisting of a refractory, which is provided freely attachably and detachably to the upper part of an injecting nozzle. CONSTITUTION:For instance, a filter mechanism 4 is provided freely attachably and detachably right above a tandish 2 nozzle 5. The mechanism 4 has many thin holes 7 having 0.5-10mm. diameter in accordance with a steel passing quantity, and is a cylindrical body 3 made of a porous refractory having 5-100mm. thickness. When a molten steel 1 such as a killed steel, etc. is injected into a casting mold 10 from the nozzle 5 through the mechanism 4, an inclusion in the molten steel adheres to the circumference of the thin hole 7 when it passes through the thin hole 7 and it is filtered. When the thin hole 7 is clogged with the inclusion, and a flow of the molten steel is obstructed, the cylindrical body is replaced with a new cylindrical body 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing inclusions from molten steel, particularly killed steel.

Conventionally, as a method for removing υ inclusions from molten steel, the following various methods have been proposed and implemented.

1) Method of blowing gas bubbles into the molten steel in the ladle 2. In this method, the molten steel is stirred by the blown gas bubbles, and inclusions in the molten steel collide, agglomerate, enlarge, and float up to be removed. Floating inclusions are carried by the upward flow of molten steel caused by gas bubbles, and are adsorbed and removed by the slag on the upper surface of the molten steel.

2) A method of blowing 7 lux into the molten steel in the ladle: This method uses flux instead of the gas bubbles described above, and in addition to the same effect, the blown flux collides with inclusions and causes damage to them. It is absorbed and floats away.

3) Method of installing a weir in the tundish: By installing a weir in the tundish (hereinafter referred to as "T/D"), the residence time of molten steel in the T/D is ensured, and during that time, inclusions are prevented from floating. This is a way to promote In addition, a modified method has been proposed in which holes are formed in the salt and molten steel is mixed and stirred to prevent p-inclusions from coagulating and enlarging and removing them by flotation.

4) Method of improving the shape of the T/D nozzle discharge hole: This method completely improves the shape of the T/D nozzle discharge hole, controls the flow of molten steel from the nozzle, and prevents inclusions from forming in the mold. This is a method to make it easier to float. Specifically, the penetration depth of the molten steel flow into the crater is made as shallow as possible.

5) Method for improving the morphology of inclusions: This method, for example, improves the morphology of inclusions by
Reduced by f? It changes from a solid phase to a liquid phase in rfA, making it easy to aggregate, and producing a sound that promotes flotation.

In addition, as a further development of the method using a T/D weir provided with holes, there is a method in which the diameter of the holes in the weir is made small and all inclusions are removed by adsorption.

As described above, the conventional method for removing inclusions is based on flotation removal using the difference in specific gravity between the inclusions and molten steel, and also involves agglomeration and enlargement of the inclusions in order to further promote flotation removal. .

Therefore, for example, in order for the inclusions to coagulate and enlarge, it is necessary to create as many chances for the inclusions to collide with each other, and as the inclusions are removed and become cleaner, the number of collisions decreases, and there is a disadvantage that it is difficult to remove them.

In addition, the method for removing flocculation regardless of whether it is agglomerated or enlarged is flotation separation, which is an extremely time-consuming process.

For this reason, when using this method, measures such as ensuring residence time in the T/D are required. On the other hand, even with the method of absorbing inclusions by blowing flux, there is a problem of the chance of collision of the inclusions J and the problem of flotation and separation.

By the way, regarding these points, the method of adsorbing and removing inclusions from molten steel using a weir with pores is a new method for removing inclusions, but if the weir in the tundish is given this function, the first method is adsorption filtration. The pores are placed in areas where the flow of molten steel is sparse, such as the cross section of the tundish, which reduces the removal efficiency.Secondly, inclusions are adsorbed to the pores in the base, making speed control impossible. It is difficult to put it into practical use if it is extremely difficult to replace it when it becomes damaged (if the pore diameter is enlarged to prevent pore blockage, the contact area with molten steel will be reduced, and the inclusion removal ability will be reduced). There are drawbacks.

As a result of various studies on a practical and efficient method for removing inclusions, the inventors found that in order to remove inclusions efficiently, it is necessary to place the inclusions on the tundish nozzle where the flow of molten steel is most dense. The present invention was completed based on the knowledge that it is essential to install the device in a detachable and easily replaceable manner.

Thus, the gist of the present invention is that the injection nozzle has a thickness of 5 to 10 mm with a large number of holes of 0.5 to 10 M in diameter on the upper part of the injection nozzle.
Detachable filter made of 100B perforated large material @
This is a method for removing inclusions in molten steel, which is characterized by providing a filter mechanism and injecting melt 4 into a mold through the filter mechanism.

The above-mentioned "injection nozzle" includes, for example, a nozzle provided in a ladle or a tundish, but since the present invention is particularly useful in continuous casting, the following description will refer to a tundish nozzle for convenience. Describe it as

1. The above-mentioned "molten steel" is not particularly limited, and due to its nature, the present invention is applicable to any molten steel where removal of inclusions is a problem, but in the case of killed steel, the effect is is remarkable.

By the way, the reason why the above filter mechanism is installed directly above the tundish nozzle in a removable and replaceable manner is as follows.
This is because this nozzle narrows the flow cross section of the molten steel, so it is easy to ensure the flow rate of the molten steel passing through the pores, and this is most effective in removing inclusions.

Further, it is a basic condition for using the adsorption filtration removal method according to the present invention that it is detachable and easy to replace.

By making it removable, a constant injection amount can be ensured at all times, but if it is not replaceable, it will be impossible to perform casting no matter where it is installed, and there is no point in removing inclusions.

In a specific embodiment of the present invention, a filter mechanism made of a perforated refractory that adsorbs and filters inclusions from molten steel has a 0.
It has a large number of holes with a diameter of 5 to 10 holes depending on the amount of steel passed through.
5i02. A40s, ZrO2, MgO or CaO
It is a cylindrical body made of refractory material whose main component is one component or a plurality of these components. This cylindrical body made of refractory is installed in a removable and replaceable manner on a tundish nozzle, and the pores in the refractory are rapidly regulated and injected into the mold, thereby absorbing and M-filtering inclusions. When the pores are clogged with inclusions and the flow of molten steel is obstructed, replace the cylindrical body with a new perforated large-sized cylindrical body.

By using the above-mentioned refractory material as a main component, it can be retained in molten steel, and the adsorption and filtration function of the filter mechanism can be further improved.

The number of holes provided in the filter mechanism made of the perforated support body according to the present invention can be appropriately set depending on the amount of steel passed through, but the diameter of the pores is limited to 0.5 to 1 Q IUL.

When the pore diameter is less than 0.5 m, the molten steel head is 50 y+
If it is below about x, it will not be possible to overcome the common surface tension of refractories and speed up. On the other hand, if it exceeds 10 Bf, the contact area between the molten steel and the refractory cannot be ensured.

Further, the thickness of the perforated resistor was set to 5 to 100B, but the maximum thickness was determined from the pressure loss of the amount of steel passed through, and the minimum thickness was determined from ensuring the durability of the refractory and the amount of adhesion of inclusions. If the thickness is less than 5 ML, the durability and amount of inclusions attached will be insufficient, while if it exceeds 100 Mti, the pressure loss will be too large.

As mentioned above, the number of holes in the large perforated material can be determined as appropriate, but preferably the flow rate of the amount of steel passing through the holes is set to 0.1 m/see.
A scrubbing speed of ~5 m/see is desirable in terms of inclusion adhesion, and therefore the number is determined depending on the casting speed and hole diameter.

For example, a filter with a pore diameter of 3U has a flow rate of 2t/mi.
n, approximately 500 pieces is appropriate.

1 and 2 of the accompanying drawings are schematic cross-sectional views illustrating a preferred embodiment of a filter mechanism for carrying out the method according to the present invention, and FIG. 1 shows the filter installed directly above a tundish nozzle. A schematic cross-sectional view showing the mechanism (a portion of the filter is a partially front view), and FIG. 2 is a partially enlarged view thereof.

In the figure, inside a tundish 2 that accommodates molten steel, preferably molten steel 1, which is killed steel, a filter mechanism 4 according to the present invention consisting of a perforated refractory cylinder 3 is installed directly above a tundish nozzle 5 so that it can be delayered. It is installed in

The perforated refractory cylinder 3 is removably attached and fixed to a lifting mechanism (not shown) protected by a sleeve brick 6.

When molten steel is injected, the molten steel in the refractory cylinder 2 enters the inside of the cylindrical body through the appropriate number of pores 7 provided over the entire circumference of the perforated refractory cylinder 3, passes through this filter mechanism, and enters the cylindrical body. Head towards Tsushu Nozzle 5. At this time, inclusions in the molten steel are filtered by adhering to the periphery of the pores when passing through the pores.

In the figure, numeral 8 is a sliding nozzle, 9 is an immersion nozzle,
And 10 indicates a continuous casting mold.

The arrangement of the pores is determined so that they are uniformly distributed over the entire circumferential surface, as shown in an enlarged view in FIG.

Next, the present invention will be explained by examples.

EXAMPLE A 70 t killed steel molten copper whose steel composition is shown in Table 1 was treated using the filter mechanism shown in FIGS. 1 and 2.

The perforated cylinder body is made of mullite (75% AljtOs,
370 pores with a diameter of 5u+ were provided over the entire circumference.

The test melt pot components in the mold are as shown in Table 1, and by applying the filter machine 41 according to the present invention, T, O, (
It can be seen that the total oxide inclusions) are reduced by half. On the other hand, the blockage situation of the filter mechanism is as shown in the graph of FIG. In order to maintain a predetermined casting speed, the opening of the sliding nozzle was increased as the flow rate decreased due to blockage, but from 4 minutes after the start of casting, the opening of the sliding nozzle for T/D was increased. It reached full capacity in 22 minutes, and the casting speed began to decrease after a while. At this point, the filter was replaced with a new one, and the opening of the T/D sliding nozzle was restored again, and casting could be completed immediately.

Figure 3 shows T, 0. Changes in are also shown.

Changes in molten steel composition due to surface inclusion filter mechanism (M amount%)
(Note) T, 0. : Total oxide inclusions As described above, according to the method of the present invention, the filter mechanism is removably provided directly above the tundish nozzle, so that even when the opening K of the tundish nozzle reaches 100%, the predetermined inclusions can be maintained. The filter mechanism can be easily replaced during the casting period, and the number of inclusions in the molten steel in the mold does not increase rapidly even during the replacement period.

Thus, the present invention is an excellent invention that can make a great contribution to this field in terms of its excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a schematic view of a preferred embodiment of the filter mechanism according to the present invention (partially a front view); FIG. 2 is a partially enlarged view of FIG. 1; and FIG. It is a graph showing changes in nozzle opening degree, casting speed, and total oxide inclusions over time from the start. 1: Molten steel, 2: Tundish, 3: Perforated person-proof cylinder, 4: Filter mechanism, 5: Tundish nozzle, 7
:pore. Applicant's agent Patent attorney Akira Hirose - Hata / [￥] 2f-3 Kuni

Claims (1)

[Claims] At the top of the injection nozzle, a removable filter mechanism consisting of a large perforated material with a thickness of 5 to 100 mm and a large number of holes with a diameter of 0.5 to 101 μL is installed, and the molten steel is injected into the mold through the filter mechanism. Features: A method for removing inclusions in molten steel.