JPH0212664B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to casting nozzles such as immersion nozzles, long nozzles, short nozzles, etc. used in continuous casting of steel. Casting nozzles are used for the purpose of preventing air and slag from getting involved, and preventing molten steel from scattering when injecting molten steel between pots and pots, between pots and a tundish, or between a tundish and a mold. Conventionally, alumina-carbon ( _Al2C3 -C) has been mainly used as _a nozzle material. However, with the recent remarkable development of continuous casting technology, there is a trend towards multiple continuous casting, and the materials used in the past are no longer showing sufficient durability. Also,
Conventional alumina-carbon materials have a disadvantage in that alumina precipitated from molten steel adheres to the inside of the nozzle hole, causing nozzle blockage. As a method to prevent this nozzle clogging, Ar or O ₂ is placed inside the nozzle hole.
Gas blowing is practiced, but manufacturing a nozzle equipped with a gas blowing mechanism is complicated, and areas where a large amount of gas blows out may cause local melting damage due to turbulent flow of molten steel. There are disadvantages such as being uneconomical. In addition, blowing gas
It is difficult to eject gas uniformly in the circumferential direction of the nozzle. On the other hand, magnesia-carbon (MgO-C) nozzles are known as another nozzle material, and this nozzle has extremely little alumina adhesion that can cause nozzle blockage, and also has excellent erosion resistance against molten steel. On the other hand, since the coefficient of thermal expansion is larger than that of an alumina-carbon nozzle, it has the disadvantage of being relatively poor in spall resistance. As a result, although magnesia-carbon nozzles have inherent effects such as corrosion resistance and nozzle blockage resistance, large and complex nozzles have drawbacks in spall resistance when operating conditions are harsh. Currently, it is not possible to use it safely and stably because it is easily exposed. The present invention was made in view of the above circumstances, and an object of the present invention is to provide a casting nozzle that has excellent corrosion resistance and spalling resistance against molten steel slag, and is free from nozzle blockage due to alumina adhesion. The present invention uses 90 to 50wt of MgO on the inner peripheral surface side of the nozzle.
This casting nozzle is made of MgO--C fired refractory containing 10 to 50 wt% of C, and the outer peripheral surface side is made of Al ₂ O ₃ --C-based fired refractory. This nozzle is effective in preventing nozzle clogging and improving the corrosion resistance of the nozzle hole by using MgO-C fired refractory on the inner peripheral surface side. In addition, although MgO-C fired refractory itself has poor spalling resistance, by using Al ₂ O ₃ -C fired refractory on the outer circumferential side, the nozzle as a whole has excellent spalling resistance. becomes. The reason why the nozzle of the present invention has excellent spalling resistance is that the Al ₂ O ₃ -C fired refractory disposed on the outer peripheral surface is a material with excellent spalling resistance. By containing carbon components on both sides, reaction between the two is prevented.
For example, on the outer circumference side made of Al ₂ O ₃ -C fired refractory, for example MgO which does not contain carbon,
If materials such as ZrO ₂ are placed on the inner peripheral surface, the structure will become denser due to reaction, reducing the spalling resistance of the nozzle. Among the nozzles of the present invention, the immersion nozzle and the long nozzle are partially immersed in molten steel, and the portion (slag line) on the outer circumference side that contacts the slag is more severely damaged than other portions. Therefore, if the portion corresponding to the slag line on the outer peripheral surface of the nozzle is made of ZrO ₂ -C fired refractory, the life of the nozzle of the present invention will be further improved. The drawings all show embodiments of the nozzle of the present invention, and in Fig. 1, the outer peripheral surface side is made of Al ₂ O ₃ -C fired refractory 1, and the entire inner peripheral surface side is made of MgO-C fired refractory. In Fig. 2, the outer peripheral surface side is made of Al ₂ O ₃ -C fired refractory 1, as in Fig. 1, and
A part of the inner peripheral surface side is made of MgO-C fired refractory 2. Figure 3 shows that the outer circumferential side is made of Al ₂ O ₃ -C fired refractory 1, and the slag line part is
ZrO ₂ -C fired refractory 3, with MgO on the inner peripheral surface side
-C-grade fired refractory 2. Figure 4 shows that the inner peripheral surface is partially covered with MgO-C fired refractory 2.
The slag line part on the outer peripheral side is made of _ZrO2 -C fired refractory 3, and the other part is made of _{Al2O3 -} C fired refractory 1. In the nozzles shown in Figures 2 and 4, part of the inner peripheral surface is made of MgO-C fired refractory;
Since the reactive gas generated from the MgO-C substance and preventing the adhesion of alumina precipitates covers the entire inner circumferential surface of the nozzle along with the molten steel flow, MgO-C fired refractories are not necessarily provided on the entire inner circumference side. This is because both are effective. Furthermore, since the MgO-C fired refractory has excellent corrosion resistance, it is preferable to provide it at the upper and lower corners where the melting loss is large, as shown in the figure. Conventional technology regarding composite nozzles includes:
(A) Jitko No. 55-32699, (B) Jitko No. 55-32700, (C)
Publications such as JP-A-54-66330 and (D) JP-A-54-155124 are listed. However, among the above (A),
(C) and (D) are characterized in that the portion corresponding to the slag line is made of ZrO ₂ -C fired refractory, and there is no mention of the material for the inner peripheral surface of the nozzle. (B)
_{( B} ), silica, alumina, zirconia, magnesia, and silicon carbide are exemplified as refractories with less adhesion of alumina precipitates. It has not been. That is, the difference between the present invention and the device of reference (B) is the difference in the material on the inner peripheral surface side. Therefore, the material of the inner peripheral surface of the nozzle is
Comparing the corrosion resistance, spalling resistance, and alumina adhesion resistance of MgO-C fired refractories and (B) magnesia refractories shown in Utility Model Publication No. 55-32700, all of them are MgO-C fired refractories. Good results can be obtained with refractories. This is because MgO-C fired refractories generate reactive gas through the reduction reaction shown by the reaction formula MgO + C → Mg↑ + CO↑ at high temperatures during operation, and this gas evaporates from the entire surface of the nozzle, resulting in alumina deposition. can be prevented. Furthermore, it is considered that corrosion resistance is excellent because slag or molten steel hardly comes into contact with or penetrates the nozzle refractory due to the generation of gas evaporation. In addition, because the nozzle of the present invention contains carbon components on both the inner and outer circumferential surfaces, there is no reaction between them despite the fact that they are made of different materials, which greatly contributes to improved spall resistance. There is. In the prior art, there is no known nozzle in which the inner circumferential surface side and the outer circumferential surface side are made of different materials, and in which both the inner and outer circumferential surfaces contain a carbon component. Next, the constituent components of each material of the nozzle of the present invention will be described. First, the MgO-C fired refractory used on the inner peripheral surface side contains 90 to 50 wt% of MgO and 10 to 50 wt% of C. Other components include Cr ₂ O ₃ , CaO, Al ₂ O ₃ ,
SiO ₂ , ZrO ₂ , Fe ₂ O ₃ , TiO ₂ , Si, SiC, Si ₃ N ₄ ,
It can contain at least 20 wt% of one or more of BN, B ₄ C, Al, Na ₂ O, K ₂ O, P ₂ O ₅ , etc.
If MgO is 90 wt% or more and C is less than 10 wt%, spalling resistance decreases and adhesion of alumina and the like increases. If MgO is less than 50wt% or C is more than 50wt%, the corrosion resistance against molten steel decreases. As the raw material used, the MgO source is generally a commercially available sintered or electrofused magnesia clinker with an MgO content of 95 wt% or more for refractories. Examples of C sources include scaly graphite, earthy graphite, carbon black, pitch, coke, coal, coke and pitch, and carbides of organic binders such as phenolic resins. The chemical components of Al ₂ O ₃ -C that make up the outer peripheral surface are:
_Al2O3 ; 40-70wt% _{, C20-40wt} %, other components include _Cr2O3 , CaO, _SiO2 , _{Fe2O3 , TiO2} , Si,
It consists of 20wt% _or less of one or more of SiC, _Si3N4 , BN, Al, _Na2O , _K2O , _{P2O5 ,} etc. Al ₂ O ₃ 40wt
% or less, corrosion resistance is poor and undesirable.
If Al ₂ O ₃ exceeds 70 wt%, the spalling resistance will decrease, which is not good. Moreover, if C is less than 20 wt%, spalling resistance decreases, and if C is more than 40 wt%, corrosion resistance is deteriorated, which are not good. As a raw material for Al ₂ O ₃ , electrofused and sintered synthetic alumina or natural and synthetic products such as bauxite, mullite, sillimanite, kyanite, etc. can be used. As a raw material for C, MgO
- Those listed in the description of C-grade fired refractories can be used. The chemical composition of the ZrO ₂ -C fired refractory that constitutes the portion corresponding to the slag line on the outer peripheral surface side is as follows:
Contains ZrO ₂ ; 30 to 90 wt%, C; 10 to 50 wt%,
Other components include Cr ₂ O ₃ , CaO, Al ₂ O ₃ , SiO ₂ ,
Fe ₂ O ₃ , TiO ₂ , Si, SiC, Si ₃ N ₄ , B ₄ C, BN,
One or more of Al, Na ₂ O ₃ , K ₂ O, P ₂ O ₃ and the like can be contained in an amount of 20 wt % or less without causing any adverse effects. As raw materials for ZrO ₂ , electrofused or sintered zirconia, natural zircon sand and its crushed products, zircon clinker, etc. can be used. Hereinafter, the manufacturing process of the nozzle of the present invention and the results of using the product will be explained with reference to Examples. Example 1 First, each compound ABC shown in Table 1 was thoroughly mixed and kneaded using a mixer to prepare a molded clay. Next, using a partition frame made of a thin plate approximately 2 mm thick in the rubber molding frame of an isostatic press, MgO-C clay was placed on the inside, Al ₂ O-C clay was placed on the outside, and ZrO ₂ was placed in the area corresponding to the slag line. - Put in each clay so that it becomes C quality clay, apply appropriate vibration to fill it, pull out the partition frame upwards, cover the top cover and seal it completely, and then place this rubber molding frame in isostat. It was inserted into the high-pressure tube of the Tsukupress and press-formed. The molding pressure is 1000Kg/ ^cm2 . The obtained molded body was placed in a pod filled with coke powder, fired at a temperature of 1000°C, cut to a predetermined size, coated with an antioxidant, and dried. As a result, the inner peripheral surface of the nozzle is covered with MgO-C fired refractory.
An immersion nozzle as shown in FIG. 3 was obtained in which the outer peripheral surface side was made of Al ₂ O ₃ --C fired refractory and the portion corresponding to the slag line on the nozzle outer peripheral surface was made of ZrO ₂ --C fired refractory.

【table】

[Table] Example 2 Using the same clay manufacturing method as in Example 1, the second
As shown in the figure, an immersion nozzle was obtained in which the outer peripheral surface was made of Al ₂ O ₃ --C fired refractory, and the inner peripheral surface was made of MgO--C fired refractory at certain intervals. Comparative Example 1 A conventionally known immersion nozzle made entirely of Al ₂ O ₃ --C fired refractory was obtained using the formulation shown in Table 1. Comparative Example 2 Al ₂ O ₃ − with the composition shown in Table 1 on the outer peripheral surface side.
The immersion nozzle was made of carbon-based fired refractory and the inner peripheral surface side was made of MgO--carbon fired refractory. Comparative Example 3 An immersion nozzle made entirely of MgO-C fired refractory was obtained using the formulation shown in Table 1. Table 2 shows the results of casting 600 tons of aluminum killed steel using the nozzles of Examples 1 and 2 of the present invention and Comparative Examples 1 and 2. Since Comparative Example 3 had significantly poor spalling resistance, no casting test was conducted. According to the results, in the nozzle of this example, almost no nozzle clogging due to alumina adhesion was observed even without argon blowing, and there was little internal hole enlargement due to melting damage. On the other hand, Comparative Examples 1 and 2 are inferior in both corrosion resistance and alumina adhesion resistance.
In particular, Comparative Example 1 was used while blowing argon gas, but was inferior to the Examples of the present invention. The spalling resistance test was limited to a table test because if the nozzle was damaged, it would cause a hot water leakage accident. The method is to heat the nozzle to 1500℃ with the same shape.
After heating for 60 minutes, it was cooled with water and the occurrence of cracks was observed. In both Examples of the present invention and Comparative Example 1, no cracking was observed and the results were good. In Comparative Example 2, slight cracks were observed, probably due to the densification of the structure due to the reaction between the inner peripheral surface side and the outer peripheral surface side. Comparative Example 3 had large cracks and was damaged. According to the present invention, as described above, the inner peripheral surface side is made of MgO-C fired refractory, and the outer peripheral surface side is made of Al ₂ O ₃ −
By using C-based fired refractories, MgO-C
It is possible to make use of the corrosion resistance and nozzle clogging prevention effect of the fired refractory, and to obtain a cast nozzle with excellent spalling resistance. Recent continuous casting technology is trending toward multiple casting, in which a single nozzle performs multiple castings, and conventional nozzle materials are no longer compatible with this trend. The present invention exhibits sufficient durability even when used in multiple casting because it has corrosion resistance, nozzle blockage prevention, and spalling resistance, which are the three major elements required for a casting nozzle. As a result, if the casting nozzle of the present invention is used, the operating rate of the continuous casting process can be significantly improved. In addition, as described above, the nozzle of the present invention can easily generate gas evenly compared to the conventional argon blowing method, and as a result, there is no problem of local melting or local damage when blowing argon gas. There is no blockage and there is no need to use expensive and complicated argon gas, which has a great effect.

[Brief explanation of drawings]

1 to 4 are explanatory diagrams of embodiment nozzles of the present invention. 1...Al ₂ O ₃ -C-based fired refractory, 2...MgO-
C-type fired refractory, 3...ZrO ₂ -C-type fired refractory.

Claims (1)

[Claims] 1. MgO 90~50wt%, C10~ on the inner peripheral surface side of the nozzle
MgO-C fired refractory containing 50wt%,
A casting nozzle whose outer peripheral surface is made of Al ₂ O ₃ -C fired refractory. 2 Insert the part corresponding to the slag line on the outer circumferential surface of the nozzle.
The casting nozzle according to claim 1, which is made of ZrO ₂ -C fired refractory.