JP2003290885A - Immersion nozzle for preventing coasening of inclusion in molten steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an immersion nozzle for preventing the coasening of inclusion in molten steel in a mold and the worsening of cleanliness by adsorbing oxide-based inclusion essentially comprising alumina in the molten steel to prevent the mixture into the molten steel and by eliminating material easily reacting with the molten steel in the inner wall of the nozzle. <P>SOLUTION: This immersion nozzle 1 uses Al<SB>2</SB>O<SB>3</SB>-C material hardly reacting with the inclusion in the molten steel on the lining part 5 of a vertical passage 6 in the immersion nozzle at the inner wall portion of the nozzle, brought into contact with the molten steel at the steel discharging hole of a tundish for supplying the molten steel into the mold for continuous casting, and on the inner wall of a spouting hole part 4 disposed at the lower part of the vertical passage 6, brought into contact with the molten steel. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for preventing the coarsening of oxide inclusions in steel, and in particular, the improvement of the immersion nozzle for feeding molten steel in continuous casting improves the coarseness of oxide inclusions in molten steel. Relating to a means for preventing aging.

[0002]

2. Description of the Related Art In the continuous steel casting method, molten steel is supplied from a ladle to a mold through a tundish. The tundish is supplied to the mold by a refractory molten steel supply dipping nozzle. During this supply, minute inclusion particles suspended in the molten steel are deposited on the refractory wall of the nozzle, the flow path of the molten steel is narrowed, and the nozzle clogging phenomenon occurs. When the inclusions are deposited on the nozzle, the deposited inclusions are peeled off, and when they are mixed in the molten steel, there arises a problem that it causes quality deterioration such as biting in the steel material.

By the way, in the nozzle, various oxide refractory materials such as quartz material, alumina material, alumina-silica-based high alumina material, zirconia-based material, zirconia-calcia-based material, etc., which are refractory materials of the nozzle, A nozzle made of the mixed material and sometimes a material mainly containing a magnesia material or an alumina-magnesia spinel material is used.
Therefore, it is said that the alumina layer formed by the reaction between these refractory materials and molten steel becomes the starting point, and molten steel containing a group of inclusions in which fine inclusion particles coalesce solidify and deposit on it. There is. As a measure to prevent this accumulation,
It has been proposed to reduce the SiO ₂ in the refractory which is the cause of the formation of the alumina layer. Further, in order to inclusions consisting mainly of aluminum to be suspended in the molten steel to the inner wall of the nozzle hole to avoid clogging of the immersion nozzle is deposited as described above, the material of the inner wall of the nozzle Zr0 ₂ -CaO-C Material There is a method to make it a refractory.

Further, as an improvement of the immersion nozzle, JP-A-4-327350 discloses that in order to prevent the immersion nozzle from being clogged, CaF is added to the alumina-based inclusions flowing into the immersion nozzle to reduce the melting point. In order to prevent clogging of the nozzle, the surface shape of the alumina-based inclusions is made spherical so that they do not coalesce and aggregate into a group of inclusions in the molten steel. In addition, JP-A-5-201776
Japanese Unexamined Patent Application Publication No. 0-202 discloses a method of preventing clogging of a nozzle by using a refractory material having a function of preventing adhesion of inclusions mainly composed of alumina. By preventing the clogging due to the deposition of the nozzles in this way, the deterioration of the quality of the steel slab that occurs when the deposited inclusions fall and mix into the molten steel is prevented.

[0005]

The oxide-based inclusions mainly composed of alumina in the molten steel form a low melting point phase with the molten steel to coarsen the inclusions, and the coarsened inclusions flow into the mold. As a result, the cleanliness of the molten steel deteriorates, and inclusions or bites in the obtained continuous cast piece adversely affect the quality.
Therefore, the problem to be solved by the present invention is to prevent the oxide-based inclusions mainly composed of alumina in the molten steel from adsorbing into the molten steel, and to easily react with the molten steel of the inner wall of the nozzle. Is provided from the inner wall surface to prevent coarsening of inclusions in the molten steel in the mold to prevent deterioration of cleanliness.

[0006]

Means for Solving the Problems In the invention of claim 1, the means for solving the above problems is the molten steel of a dipping nozzle for a tundish tap, which supplies molten steel to a mold for continuous casting. A submerged nozzle that prevents the inclusion of coarse particles in molten steel and prevents coarsening of inclusions, characterized by using an Al ₂ O ₃ -C material that does not easily react with inclusions in molten steel in the inner wall portion of the nozzle that comes into contact with .

According to a second aspect of the present invention, the inner wall portion of the nozzle that comes into contact with the molten steel is the lining portion of the vertical passage in the immersion nozzle and the discharge port portion arranged at the lower portion of the vertical passage. The immersion nozzle prevents inclusion of inclusions in the molten steel described above and prevents coarsening of inclusions.

That is, since the lining portion of the nozzle inner vertical passage of the inner wall portion of the immersion nozzle and the discharge port or the inner wall of the discharge port are in direct contact with the molten steel, the chemical reaction with the inclusions in the molten steel occurs at the interface. To form a low melting point phase, which are mixed in the molten steel to form coarse inclusions. Therefore, the material of those portions is made a material that does not easily react with the inclusions in the molten steel, and the principle thereof is as follows.

Alumina present in molten steel has poor wettability with molten steel and tends to be discharged out of the system. Utilizing this property, the refractory in the part where the molten steel and the immersion nozzle contact each other has poor wettability with the molten steel and good wettability with alumina, and the alumina-based inclusions passing through the immersion nozzle are used as the inner surface of the immersion nozzle. To prevent it from flowing into the mold. By the way, in the conventional ZrO ₂ -CaO-C refractory, it reacts with alumina and CaO on the inner surface of the nozzle,
A low melting point phase is formed and inclusions are coarsened. However, in the invention of the present application, the inner wall of the immersion nozzle that contacts the molten steel is made of Al.
By using a refractory material of ₂ O ₃ -C material, the reaction between molten steel and this refractory material is suppressed, and coarsening of inclusions can be prevented.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the immersion nozzle 1. The immersion nozzle 1 is a body part 2 attached to a tap hole at the bottom of a tundish, a powder part 3 penetrating powder in a mold and immersed in molten steel, and a nozzle part in the nozzle. The main body 2 and the powder portion 3 around the discharge passage portion 4 arranged at the lower end portion of the vertical passage 6 and a plurality of discharge outlets 7 which are horizontally exposed from the lower end of the vertical passage 6 and which regulate the vertical passage 6. An inner lining portion 5 is arranged on the inner wall portion of the nozzle.

In this embodiment, the lining portion 5 around the vertical passage 6 in the nozzle inner wall portion which comes into contact with the molten steel 8 passing through the immersion nozzle 1 at the tapping mouth at the bottom of the tundish for supplying molten steel to the mold for continuous casting. And Al ₂ O ₃ -C which is less likely to react with the inclusions in the molten steel 8 at the discharge port 4 arranged at the bottom of the vertical passage 6.
Formed from material. That is, the vertical passage 6 which is the passage for the molten steel 8 inside the immersion nozzle 1 and the inner wall portion of the discharge port 7 are formed of an Al ₂ O ₃ —C material which is difficult to react with the inclusions in the molten steel 8.

By doing so, the fine alumina-based inclusions in the molten steel 8 passing through the immersion nozzle 1 are adsorbed on the Al ₂ O ₃ -C material which is the inner wall material of the lining 8 and the discharge port 4. Furthermore, CaO that reacts with alumina-based inclusions is eliminated from the inner wall surface of the nozzle to prevent fine alumina-based inclusions from mixing in the molten steel 8 injected into the mold, and to react with CaO to reduce It is possible to form a melting point phase to prevent coarsening of inclusions, and to eliminate coarse inclusions that form sand marks from the obtained continuously cast steel slab.

[0013]

[Example] Table 1 shows the material of the tundish dipping nozzle 1.
It was formed as the material shown in. That is, in the conventional product, the lining portion 5 of the inner wall of the nozzle that comes into contact with the molten steel 8 of the immersion nozzle 1 is used.
ZrO ₂ —CaO—C material is used for the discharge port 4 and the test product A has Al ₂ O ₃ —C material for the lining 5 and the discharge port 4
The ZrO ₂ —CaO—C material was used for the test piece B, and the test product B used the Al ₂ O ₃ —C material for both the lining portion 5 and the discharge port portion 4.

[0014]

[Table 1]

CrMo alloy steel JIS SCM435 was melted in a 150 t electric furnace, smelted in a ladle, degassed, and then stranded into a tundish dipping nozzle.
Test pieces A and B made of the material shown in Fig. 3 and conventional ones are continuously cast using three types of immersion nozzles, and the obtained steel pieces are heated in a heating furnace and slab-rolled into steel pieces of φ65 Was produced.

Next, the three types of immersion nozzles used above were taken out and observed, and the results are shown in Table 2. 85 to 88% of the deposits on the linings of the test products A and B and the deposits on the discharge port of the test product B are made of Al ₂ O ₃ , and they may adsorb alumina in the molten steel. Recognize. However, almost no reaction was observed between the refractory material in the lining portion and the discharge port and alumina in the molten steel.

On the other hand, in the test product A, there was no deposit on the discharge port, and the reaction between the refractory material at the discharge port and alumina in the molten steel was observed on the steel slab. The composition of the reaction phase is Al ₂ O ₃ : 50-80
%, CaO: 20-40%, and a low melting point phase was formed.

No deposit of alumina was found in the conventional product. However, the reaction between the refractory at the lining and the discharge port and the alumina in the molten steel was observed in the billet. The composition of the reaction phase is Al
_A low melting point phase was formed with ₂ O ₃ : 50 to 80% and CaO: 20 to 40%. Shown in.

[0019]

[Table 2]

With respect to the three test pieces of φ65 produced from the continuous cast pieces by the above-mentioned test product A, test product B and conventional product immersion nozzle, the detection results of the oxygen value and the inclusion index with the conventional product as 100 are shown. It shows in Table 3. As a result, compared to the conventional product, the test product A did not show a significant improvement in the inclusion index, but the test product B showed the improvement effect.

[0021]

[Table 3]

Further, Table 4 shows the size and composition of coarse inclusions detected from the above three types of test pieces. As a result, the inclusion compositions detected in the conventional product and the test product A show almost the same composition, which is very similar to the reaction phase composition of the low melting point phase formed on the inner wall of the immersion nozzle. this is,
It is considered that the inclusions became coarse due to the reaction with the material of the immersion nozzle. On the other hand, in the test product B, the detection of inclusions exceeding 20 μm was not observed.

[0023]

[Table 4]

From the results of the test product B, the material of the inner wall of the immersion nozzle is made of Al ₂ O ₃ in the invention of the present application.
The use of the -C material has been shown to be the best.

[0025]

As described above, according to the present invention, by using the Al ₂ O ₃ -C material as the material of the nozzle inner wall portion which is in contact with the molten steel of the immersion nozzle of the tundish tap in continuous casting, The slab does not contain coarse inclusions,
The present invention has excellent effects that have not been obtained in the past, such as the cleanliness of steel materials being improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an immersion nozzle.

[Explanation of symbols]

1 immersion nozzle 2 body 3 powder section 4 Discharge port 5 Liner 6 vertical passages 7 outlet 8 Molten steel

Claims (2)

[Claims] 1. Al ₂ O ₃ which is hard to react with inclusions in molten steel at the nozzle inner wall portion which comes into contact with the molten steel of the immersion nozzle of the tundish tap for supplying molten steel to a mold for continuous casting
A submerged nozzle that prevents the inclusion of molten steel and coarsens inclusions, which is characterized by using a -C material. 2. The molten steel according to claim 1, wherein the nozzle inner wall portion which comes into contact with the molten steel is a lining portion of a vertical passage in the immersion nozzle and a discharge port portion arranged at a lower portion of the vertical passage. The immersion nozzle prevents inclusions from entering and prevents inclusions from coarsening.