JPH0466251A - Method for preventing involution of slag into molten steel - Google Patents

Abstract

PURPOSE:To prevent involution of slag into molten steel by making depth of tundish only at pouring part in the tundish deep and damping energy in pouring stream to vertical direction. CONSTITUTION:In the tundish 12, where the molten steel 2 in a ladle is poured and flows out into a continuous casting mold, the deep part 14 in the vessel making the pouring part deep, is arranged. By using the tundish 12, even at the time of lowering 4 the molten steel surface level in the case of exchanging the ladle, as the sufficient depth to the stream pouring into the tundish 12 is secured at the position of pouring nozzle 1, the damping of energy in the pouring stream to gravity direction is made large, and even in the case the pouring stream reaches bottom face in the tundish 12, the flowing velocity is made low, and as this turn-over flowing velocity is low, too, mixed quantity of the slag in the ladle is reduced. Further, if necessary, by impressing static magnetic field or shifting magnetic field at the deep part 14 in the vessel, artificially the pouring flowing velocity can be further reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for promoting the separation of nonmetallic inclusions such as slag in molten steel.

<Prior Art> It has been known that impurities such as non-metallic inclusions in molten metal cause product defects and operational obstruction. For this reason, methods have been adopted in which the average residence time of molten steel within the tundish is increased by increasing the size of the tundish, thereby promoting flotation and separation of nonmetallic inclusions.

In particular, for the separation of slag-based non-metallic inclusions, it is important to ensure the surface level within the tundish.

On the other hand, in recent continuous casting processes, continuous casting has become increasingly popular from the viewpoint of cost benefits and improvements in operation and productivity. However, in the case of successive casting, the level of the molten metal in the tundish decreases after pouring the molten steel in the previous ladle (hereinafter referred to as the ladle) and by the time the next ladle is opened. It becomes difficult to separate the sand (such as silica sand) and pot slag packed into the pot nozzle that enters the tundish when it is opened, inside the tundish. In addition, when replacing the pot, the injection amount was larger than during normal operation in order to restore the surface level in the tundish, making it easier to get slag involved, which caused an increase in the amount of non-metallic inclusions when replacing the pot. .

A method of applying a static magnetic field to the tundish to control the flow within the tundish and prevent short circuits has also been considered. For example, 5teel r
search 59 (1988) Vol, 9 p.
, 399. In this case, in order to prevent short circuits, it is necessary to apply an electrostatic field to the entire surface in the height direction of the scene with a certain width, so the magnetic field generator needs to be large and have a large capacity, and it is difficult to apply it to production equipment. The problem remains.

Furthermore, Japanese Patent Application Laid-Open No. 62-183947 discloses a weir that separates a flotation area where slag in molten steel is floated and separated, and an outflow area where molten steel flows into a mold, and a weir that separates slag in the flotation separation area. A technique is disclosed for preventing slag entrainment by a tundish of a continuous casting machine, which is interposed in the i/fM scene, has a long nozzle inserted, and a pipe into which molten steel is injected. However, even with this method, the reverse flow of the injection flow promotes scene fluctuations in the tundish, and the flux around the injection pipe and floating nonmetallic inclusions are involved, so that a complete effect cannot be obtained.

<Problem to be solved by the invention> In conventional kundein tsuyu, due to the drop in the hot water level that occurs when changing the ladle, entrainment of tundine flux and contamination of ladle slag easily occur, compared to slabs under normal conditions. The amount of inclusions increased significantly, leading to a decline in product quality.

The present invention was made in order to provide a technology that can dissipate the energy of the injection flow in the height direction even when the scene level decreases when replacing the pot, and prevents the entrainment of tundane flux and the mixing of pot slag. It is.

<Means for Solving the Problems> The present invention provides a method for preventing entrainment of slag floating on the surface of a molten steel bath in a tundish into which molten steel is injected into a ladle and flows into a continuous casting mold. Only by deepening the tandish depth,
A method for preventing slag entrainment in molten steel, characterized by attenuating the energy of the injection flow in the vertical direction, and in the method described in the previous section, the method is characterized by applying a static magnetic field deep into the container where the molten steel is poured. In the method for preventing slag entrainment in molten steel, and in the method described in the previous section ■? 8. This is a method for preventing slag entrainment in molten steel, which is characterized by applying a moving magnetic field deep into a container for pouring steel.

<Function> As a result of water model experiments and flow analysis simulations for the tandish, it was found that the phenomenon of entrainment of pot slag in the tandish and the entrainment of flux on the surface of the tundish is due to the large flow of injection from the pot to the tundish. We learned that this is largely due to energy. In other words, if the surface level of the tundish 12 is not sufficiently secured, the large energy of the injected flow will not be dissipated in the depth direction of the tundish, resulting in a fast flow that reaches the bottom of the tundish and changes its direction to the outlet. (referred to as Show 19-Kit L3) (see Fig. 5), and it was found that the slag from the pot and the slag 5 were easily drawn in.

From this knowledge, we came to the idea that for the separation of non-metallic inclusions, it is extremely important to dissipate the euphorgy in the flow injected into the Kundeintsuyu at a position away from the Tanditsu outlet.

By using the tundish with the deep injection part and the container deep part 14 according to claim 1, the injection flow into the tundish can be ensured at a sufficient depth at the pouring nozzle position even when the level drops when replacing the pot. As a result, the energy of the injection flow is dissipated in the direction of gravity, and even when the injection flow reaches the bottom of the tundish, the flow velocity is small, and the reverse flow velocity is also small, so the injection flow is directly connected to the outlet. It becomes difficult to form a circling 13, and the amount of pot slag mixed in when replacing the pot is also reduced.

Using a kundeintsuyu that applies a static magnetic field in the deep part 14 of the container according to claim 2 is a method of artificially reducing the injection flow rate by electromagnetic force. The electromagnetic force used in this method may be a static magnetic field or a moving magnetic field.

In the case of an nMi field, a magnetic field is provided below the pouring nozzle to reduce the pouring flow rate.

In the case of a moving magnetic field, the injection flow rate from the pouring nozzle is reduced by colliding the injection flow with the upward flow caused by the moving magnetic field. However, in this case, the flow velocity due to the moving magnetic field needs to be smaller than the injection flow velocity. This is because if the flow velocity of the upwardly moving magnetic field is high, it will cause fluctuations in the tampu-inotsuyu scene, causing entrainment of the franks.

Furthermore, by using electromagnetic force, a very large turbulent flow field is formed at the location where the injection flow collides with the upward flow caused by the moving magnetic field, which promotes the coalescence and aggregation of nonmetallic inclusions and deoxidizes them. It also has the effect of increasing speed.

<Example> Using the tap inoche shown in FIG. 4, the effects of the present invention were tested.

Molten steel (low carbon aluminum killed!jl) 100 tons was passed through at an average rate of about 1 ton/m, and the molten steel flowing out under each condition was sampled to investigate the total oxygen content and nonmetallic inclusions by slime extraction method. When a static magnetic field is applied, it is approximately 1500 Gauss at the center position in the width direction of the tanditsu.
It generates a magnetic flux of s (when the core is empty).

When a moving magnetic field is applied, a magnetic flux of approximately 150 Gauss is generated at the center position in the width direction of the tray.

Further, in order to clarify the effects of the present invention, as a comparative example, an experiment was conducted under similar conditions using a normal scene level constant (300 m) tundish, and the results were compared.

The results are summarized in Table 1. As is clear from Table 1, compared to Comparative Example 1, in all of Examples 1 to 5, the amount of large nonmetallic inclusions with a diameter of 50 nm or more was lower, and the total amount of oxygen was also lower. I understand that.

Table 1 FIG. 1 is a conceptual explanatory diagram of the method according to claim 1, FIG. 2 is a conceptual explanatory diagram of the method according to claim 2, and FIG. 3 is a conceptual explanatory diagram of the method according to claim 3. It is.

FIG. 4 is a schematic diagram showing the dimensions of the tundishu described in the example (al is a front view, (b) is a side view, and FIG. 5 is a conceptual illustration of when changing the pot of a conventional tundishyu. be.

<Effects of the Invention> According to the present invention, it is possible to prevent pot slag and tundane slag from getting caught up when changing the pot, promoting cleaning of slabs when changing the pot, and improving the quality of the product. I can do it.

[Brief explanation of the drawing]

1... Pouring nozzle, 2... Molten steel, 3... Steady state level, 4... Level when the pan replacement scene is lowered, 5... Tanday 7th grade, 6... Molten steel Flow velocity vector, 7... Flow velocity hector of nonmetallic inclusions, 8... Outflow nozzle, 9... Tundish lid, 10... Static magnetic field generator, 11... Moving magnetic field generator, 12...・Tandish, 13...Short circuit, 14...Deep part of the container.

Claims (1)

[Scope of Claims] 1. In a method for preventing entrainment of slag floating on the surface of a molten steel bath in a tundish into which molten steel is injected into a ladle and flows into a continuous casting mold, only the injection portion of the tundish has a tundish depth. A method for preventing slag entrainment into molten steel, which is characterized by attenuating the energy of the injection flow in the vertical direction by increasing the depth of the injection flow. 2. A method for preventing slag entrainment into molten steel according to claim 1, characterized in that a static magnetic field is applied deep into the container into which molten steel is poured. 3. A method for preventing slag entrainment into molten steel according to claim 1, characterized in that a moving magnetic field is applied deep into the container into which molten steel is poured.