JPH07102436B2 - Nozzle for continuous casting containing calcium zirconate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory composition of a nozzle for continuous casting of steel grades and highly clean steel which contains steel, particularly aluminum and is apt to cause clogging of nozzle holes by alumina.

[0002]

2. Description of the Related Art As a nozzle for continuous casting of steel, a ladle-
There are long nozzles that connect the tundish, tundish nozzles that connect the tundish and mold, and immersion nozzles. Among them, particularly long long nozzles and immersion nozzles, spalling resistance, abrasion resistance, corrosion resistance The demand for is severe.

At present, alumina-silica-graphite, alumina-graphite,
A zirconia-graphite nozzle is used.By combining alumina and zirconia aggregate particles with high strength and high corrosion resistance with silica particles and graphite with excellent spalling resistance, spalling resistance and It satisfies the requirements for wear resistance and corrosion resistance.

However, when these nozzles are applied to aluminum-containing steel, alumina produced by oxidizing aluminum in the steel is deposited and deposited on the surface of the nozzle to block the flow path of the nozzle, so-called nozzle blockage. Is likely to occur. Further, when used for highly clean steel containing few impurities, Al, Si, etc. in the refractory forming the nozzle are impurities to the steel, which is not preferable.

As a means for solving this problem, Japanese Patent Application Laid-Open No. 57-
No. 71860, CaO is added to the refractory forming the nozzle.
It has been disclosed that the inclusion of the compound has an excellent effect of preventing nozzle clogging.

[0006] This forms a compound of CaO and Al ₂ O ₃ having a liquidus formation temperature which is considerably lower than the solidification temperature of steel, and since it exists as a low melt in molten steel, it must be precipitated and deposited. It is said that there is no. Also, Ca
Non-metallic inclusions containing O easily float in molten steel,
It is rarely incorporated as an impurity in steel, and Ca
On the surface of the nozzle refractory containing O, Al ₂ O ₃ dissolves in the molten steel as a CaO-Al ₂ O ₃ compound without precipitation and deposition, and the effect that it rarely remains as an impurity in the steel is also obtained. It is said that it can be played.

The inventors of the present application, in order to take advantage of the effect of the addition of CaO, and to eliminate the disadvantages of high thermal expansion and reactivity with water, that is, digestibility, the inventors of the present invention have used ZrO ₂ in combination. Compound CaZrO
₃ (calcium zirconate) is blended to reduce expansion,
Furthermore, 0.5 to 5 group III and IV oxides in the periodic table are used.
Proposed to add by weight% and achieved certain results.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Group III and IV of the periodic table of ₂ , ₂ , TiO ₂ , Al ₂ O ₃ etc.
Group Oxides are not a problem in general steel, but become impurities in high-purity, high-cleanliness steel, and from refractory materials that form nozzles during continuous casting of molten steel whose purity has been raised to the limit in the refining process. It is not preferable because those impurities are mixed.

When calcium zirconate containing a large amount of SiO ₂ , TiO ₂ , Al ₂ O _{3 and the} like is used as a raw material for the nozzle, a CaO-SiO ₂ -Al ₂ O ₃ -based low-melt material is produced and the nozzle is It impairs the fire resistance of refractory materials, making it difficult to use for a long time.

The problem to be solved in the present invention is to solve the problem of a nozzle made of a refractory material containing calcium zirconate together with a small amount of group III and group IV oxides in the periodic table, and to improve the steel type containing aluminum and Another object of the present invention is to provide a refractory composition that can be applied to high-purity steel and can be used for a long time, which is suitable for a nozzle.

[0011]

Regarding the calcium zirconate clinker used in the present invention, from commercially available reagents, CaO: 31% by weight, ZrO ₂ : 69% by weight.
As a result of investigating the digestibility of the calcium zirconate-based clinker prepared so as to be calcined at 1600 ° C., the following findings were obtained.

Impurities in commercially available reagents are generally Si,
Almost all oxides of Al, Ti, Fe, and B, Sc, Ga, Ge, which are group III and IV elements of the periodic table.
Sn, Pb, etc. are scarcely contained. This also applies to natural baddelite and limestone raw materials.

SiO ₂ , TiO ₂ , A as impurities
The sintered body containing 0.2% or more of the total amount of l ₂ O ₃ does not show the digestion phenomenon, but when the impurities are less than that, the digestion phenomenon is seen.

From this, it was found that it is possible to obtain calcium zirconate without a digestive phenomenon with a trace amount of additives. However, if the reagent is used as a raw material, the nozzle becomes very expensive. Therefore, the production of calcium zirconate by the electrofusion method was examined.

Calcium zirconate produced by the conventional electrofusion method is a mixture of natural baddelite and a limestone-based raw material, which is then electromelted. However, commercially available baddelite and limestone-based raw materials contain SiO ₂ , TiO ₂ , and A as impurities.
1 ₂ O ₃ and Fe ₂ O ₃ , and the total amount thereof is 0.5 to 1.
It is about 5%. Therefore, when simply electrofused, SiO ₂ , TiO ₂ , and Al ₂ O in calcium zirconate are used.
The total amount of ₃ is 0.5% or more, which is about the same as the conventional technique.

For this reason, the present inventor has conducted various studies on electrofusion methods.

It is a method in which the melting time at the time of electrofusion is made longer than in the conventional case to reduce and volatilize oxides such as SiO ₂ and TiO ₂ having a weak oxygen bonding force. When the melted material is decomposed in the electromelting process and the amount of SiO ₂ and TiO ₂ is reduced, and the electromelting operation is terminated, calcium zirconate containing less impurities is obtained. In addition, if the dissolution time is short, segregation of components occurs in the melt, and free CaO remains and causes digestion. However, this new method lengthens the dissolution time to make the melt homogeneous. It is possible to reduce the free CaO.

However, when carrying out this electrofusion method,
When the amount of Fe oxide in the raw material is large, the electrode carbon is largely worn out, which makes it difficult to perform a good electrofusion process. As a result of various studies, the content of Fe oxide is preferably 0.5% or less, and it is particularly necessary to use the badelite that has been sufficiently deironed. Note that MgO, which is unavoidably contained in the limestone-based raw material, does not hinder the electrofusion process.

From the above examination results, it is possible to obtain calcium zirconate at a relatively low cost, and the obtained raw material clinker contains 16 to 35% by weight of CaO and Al.
0.2% by weight based on the total amount of ₂ O ₃ and SiO ₂ and TiO _2.
Or more and less than 0.5 wt%, oxide 0.5 wt% or less of Fe
It is defined as a calcium zirconate clinker containing below and having CaZrO ₃ as a main component as a mineral composition.

That is, the casting nozzle according to the present invention is
16 to 35% by weight of CaO, 0.2% by weight or more and 0.5% by weight or less in the total amount of Al ₂ O _3, SiO ₂ and TiO _2.
Mitsuru, contained the following oxide 0.5 wt% of Fe, CaZrO ₃ 10 to 95 wt% of calcium zirconate-based clinker mainly composed of a mineral composition, 5 to 40 wt% graphite, other refractory material It is characterized by comprising 50% by weight or less . In addition, 1% by weight of metallic silicon
It can be contained below.

As another refractory material, zirconia, magnesia or the like may be added to improve the corrosion resistance.

The refractory composition is kneaded with an organic binder, molded, and fired in a non-oxidizing atmosphere to produce a nozzle.

[0023]

The nozzle using this clinker contains CaO, so that Al ₂ O ₃ and Ca precipitated from the steel
O reacts with the surface of the nozzle, by dissolving in the molten steel as CaO-Al ₂ O ₃ compound, it is possible to prevent the nozzle clogging. Moreover, the content of Al ₂ O ₃ and SiO ₂ and TiO ₂ as impurities in the steel is much smaller than that of the conventional nozzle, which is advantageous for casting of high-purity steel.

Regarding the content of the calcium zirconate clinker for the nozzle, if the content is less than 10% by weight, the sufficient effect of preventing nozzle clogging cannot be obtained, and if it exceeds 95% by weight, the content of graphite becomes small, so that the resistance is low. The spalling property deteriorates. The content of the calcium zirconate clinker is suitably 10 to 95% by weight.

Next, regarding graphite, graphite is used to impart spalling resistance and slag resistance.
If it is less than 40% by weight, the spalling resistance is inferior, and if it exceeds 40% by weight, the dissolution into molten steel and the soft nature of graphite become dominant, and the problem of wear due to abrasion occurs. The graphite content is suitably 5 to 40% by weight. As the type of graphite, scaly graphite, earthy graphite, quiche graphite and the like can be used, but from the viewpoint of spalling resistance and corrosion resistance, it is preferable to use natural scaly graphite. It is also important to select scaly graphite containing few impurities.

Metallic silicon may be added as a sintering agent for preventing the oxidation of graphite and developing the strength of the nozzle, and the amount is preferably 0 to 1% by weight.

[0027]

[Examples] The nozzles were obtained by mixing and molding the formulations shown in Table 1 with a binder and firing the mixture in a non-oxidizing atmosphere.
The compositions of Examples 1 to 3 all have good corrosion resistance, A
It showed the effect of preventing l ₂ O ₃ adhesion. It can be seen that the characteristics of the conventional nozzle refractory shown in the comparative example are inferior to those of the present invention.

Table 2 shows calcium zirconate as a blending raw material. Calcium zirconate A is within the scope of this invention and calcium zirconates B, C and D
Is out of range. Calcium zirconate A has a low content of impurities, and good results can be expected for molten steel with high purity.

[0029]

[Table 1]

[0030]

[Table 2]

1A, 1B, and 1C show examples of nozzles formed by using refractories having the compositions of Examples 1 to 3 shown in Table 1. The nozzle 1 in FIG. 1A is a tundish nozzle that is entirely formed of a refractory material having the composition of Example 1 in Table 1. In the nozzle 2 of FIG. 3B, the nozzle hole inner surface portions 21 and 22 are formed of a refractory material having the composition of Example 2 in Table 1, and the upper and lower outer surface portions 23, 24 and 25 are made of alumina-graphite. This is a dipping nozzle in which the outer surface portion 26 of the central portion is formed of a zirconia-graphitic refractory material. (C) of the figure
In the nozzle 3 of No. 3, the lower portions 31 and 32 are formed of a refractory material having the composition of Example 3 in Table 1, the upper 33 parts are formed of alumina-graphite, and the central portion 34 is formed of a zirconia-graphite refractory material. Is.

[0032]

EFFECTS OF THE INVENTION The nozzle of the present invention, by containing CaO, causes Al ₂ O ₃ and CaO precipitated from the steel to react on the surface of the nozzle, and the reaction compound dissolves in the molten steel to cause nozzle clogging. Al ₂ O ₃ and SiO ₂ and TiO ₂ as impurities for steel while effectively preventing
Is much lower than conventional nozzles, which is advantageous for casting high-purity steel.

[Brief description of drawings]

FIG. 1 is a sectional view showing a nozzle of an embodiment of the present invention.

[Explanation of symbols]

 1,2,3 nozzle 21,22 nozzle hole inner surface portion 23,24,25,26 outer surface portion 31,32 lower portion 33 upper portion 34 central portion

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyoto Kasai 1-1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corp. (56) Reference Japanese Patent Publication 2-23494 ( JP, B2)

Claims (2)

[Claims] 1. CaO of 16 to 35% by weight, Al ₂ O ₃
And the total amount of SiO ₂ and TiO ₂ is 0.2% by weight or more,
Calcium zirconate clinker containing CaZrO ₃ as a main component in an amount of less than 0.5% by weight , Fe oxide of 0.5% by weight or less, 10 to 95% by weight, graphite 5 to 40% by weight, and others. No. 50% by weight or less of the refractory raw material, and a nozzle for continuous casting containing calcium zirconate. 2. A contract containing less than 1% by weight of metallic silicon.
For continuous casting containing calcium zirconate according to claim 1.
nozzle.