JPS6050748B2 - Manufacturing method of highly corrosion resistant continuous casting nozzle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nozzle for casting molten metal, particularly steel.

Typical nozzles for steel casting include long nozzles and immersion nozzles that connect the steelmaking ladle and tundice mold, and are used for purposes such as preventing oxidation and scattering of molten steel. It is a particularly important refractory for continuous casting.

When these continuous casting nozzles are used, they are rapidly heated from inside the nozzle by the flow of molten steel, so a large temperature difference occurs between the inner wall and the outer periphery, and the inside of the material is subjected to large thermal stress due to the difference in expansion. For this reason, in particular, (1) excellent thermal shock resistance is required. Furthermore, since the nozzle inner hole is exposed to severe wear due to the flow of molten steel accompanied by air entrainment due to seal leakage, (2) it is required to have excellent wear resistance and oxidation resistance. Furthermore, in normal continuous casting methods, the lower end of the nozzle is immersed in molten steel. (3) Excellent slag erosion resistance is required. Conventionally, fused silica, alumina-graphite, etc. have been used as the nozzle material for continuous casting, but recently the latter, alumina-graphite, has been used in Japan's steelmaking process, which has been trending towards multiple casting. Graphite has become the mainstream because it is superior to the former in its corrosion resistance.

However, in this alumina-graphite material, among the characteristics required for the nozzle mentioned above, there is a reverse relationship between (1) thermal shock resistance and (2) and (3) abrasion resistance and corrosion resistance. Conventionally, in order to improve thermal shock resistance, when the proportion of graphite, which has excellent properties, was increased, the properties (2) and (3) were inferior, and sufficient durability could not be obtained. If alumina, which has excellent strength and corrosion resistance, is increased in order to increase durability, the thermal shock resistance (1) decreases and the risk of cracking increases, making it unusable. The current situation is that the durability has reached a plateau. The present invention overcomes the drawbacks of these conventional nozzles and has succeeded in developing a material that has excellent thermal shock resistance and corrosion resistance at the same time, and the details thereof will be described below.

The main mineral phase in the present invention consists of corundum and monofamily zirconia, and the chemical composition is Al2O.

The refractory raw material having a weight of ZrO of 80 to 2% and a weight of 2 to 2% of ZrO is hereinafter referred to as AZ.

AZ raw material has a structure in which monoclinic zirconia is dispersed in corundum crystals, and although there is no big difference in particle strength compared to normal corundum raw materials, it has a low elastic modulus and is a raw material with high thermal shock resistance. It is. Also, corundum is usually 1
While it shows an expansion of about 0.8% at 0000C, this A
The Z raw material has a low coefficient of expansion of about 0.75% and has a property that its coefficient of expansion becomes even smaller at high temperatures, so even when combined with graphite, the thermal shock resistance is greatly improved compared to conventional materials. Detailed data about the AZ raw material is shown in Table 1. By using an appropriate amount of this M raw material, the above-mentioned (
1) It can be expected that thermal shock resistance will be greatly improved.
Next, item 2 (2) required for the casting nozzle mentioned above.
Regarding wear resistance, in the conventional A'203-graphite material, in order to prevent aggregate particles from falling off due to wear of molten steel on the working surface, a small amount of SlO2 component is added, and Ae2O3
-While covering the working surface with SiO2-based melt, Ae
A common method was to make it easier for 2O3 particles to sinter together.

However, in the Ae2O3-SiO2 system, there is a problem that the melting point is lowered by components such as MnOlFeO coming from molten steel, and the viscosity on the operating surface is reduced, promoting melting loss of refractories. It is a material that is easily affected by temperature, and often causes problems due to rapid melting. However, in the AZ-graphite according to the present invention, adding an appropriate amount of SiO2 component is of course effective and produces the above-mentioned effects, but in addition, adding an appropriate amount of SiO2 component is effective.
In the 2O3-SiO2-based melt, tiny ZrO2 particles from AZ are suspended and suspended, increasing the viscosity of the liquid, completely protecting the working surface, and making it difficult to be washed away by the molten steel, making it difficult to use with conventional nozzles. It is possible to impart unprecedented wear resistance and stability against changes in steel type to the material.

Moreover, this viscous molten layer is of course effective in protecting the carbon in the material from the 02 contained in the steel and also from the 02 coming from air due to a seal failure at the top. Finally, regarding (3) slag erosion resistance,
It is well known that ZrO2 is inherently less susceptible to corrosion by slag, and exhibits strong corrosion resistance not found in other refractory raw materials, especially at the molten steel-slag interface.The casting nozzle of the present invention also has higher corrosion resistance than conventional ones. It was confirmed that it exhibits corrosion resistance.

Next, regarding the chemical composition of the M raw material, if A'203 is less than 8 weight percent, it is not preferable because useful properties such as strength and hardness, which corundum usually has, will be markedly reduced.
If it exceeds this, the superiority of conventional corundum raw materials in the above-mentioned points (thermal shock resistance, abrasion resistance, corrosion resistance) will no longer be apparent.

Similarly, when ZrO2 is less than 2% by weight, the effect is weak, and when it exceeds 2% by weight, the particle strength decreases.
Due to the strong influence of abnormal expansion of O2 (monoclinic type), it is difficult to manufacture large-sized products, so preferably 4 to 15
A range of weight percent is suitable. Further, as a method for producing the raw material, an electrofusion method, a sintering method, etc. are generally considered, but such methods are not particularly mentioned in the present invention. However, considering the current technology and price aspects,
Melting in an electric furnace is advantageous. In addition, main minerals include corundum and monoclinic zirconia, but cubic zirconia due to the inclusion of impurities, A'
Even if a small amount of 203-SiO2 glass is contained, the characteristics of the raw material will not change significantly. Next, if the usage ratio of such AZ raw materials is less than 10% by weight,
If the various raw material properties described above are not utilized, and if the amount exceeds 7%, the amount of graphite to be combined becomes too small, resulting in insufficient thermal shock resistance. In addition, if the amount of graphite is less than 2%, the thermal shock resistance will not be sufficient as described above, and if the amount of graphite is less than 4%,
If the
Since sufficient strength cannot be imparted, it becomes more likely to break. In addition, the remaining refractory aggregate powder is Ae2O3, zrO2, M, which is usually used in the refractory industry.
gO, cr2O3, caO, siO2 and these 2
Any material may be used, such as a refractory raw material made by mixing two or more species, but A with appropriate corrosion resistance and coefficient of thermal expansion may be used.
Those using e2O3 are easy to put into practical use. moreover,
In the present invention, it is more effective to contain the SiO2 component in an amount of 1 to 10% by weight for the purpose of stabilizing the operating surface and adjusting the coefficient of thermal expansion.

If this amount is less than 1% by weight, the effect will be small, and if it exceeds 2% by weight, the corrosion resistance will not be sufficient.
In the present invention, hot strength imparting agents include silicon, clay, etc. that are normally used for refractories containing carbon, as well as aluminum, BN, B4C, SiC, etc. When added as necessary, the performance of the nozzle can be further improved. can be raised.

In addition, as organic or inorganic binders, various binders commonly used in the refractory industry, such as various resins, tar pitch, silicates, and phosphates, can be considered; In terms of ease of production, phenolic resin is optimal. In addition, for the kneading process and subsequent steps, all methods normally used in the fireproofing industry can be applied to the present invention.
Regarding firing, to prevent the graphite in the base from being oxidized,
It is necessary to carry out in a non-oxidizing atmosphere.

Next, examples of the present invention will be described.

Table 2 shows the results of manufacturing various nozzles using AZ raw materials.
Shown below. All products are manufactured using phenolic resin, which is kneaded using a high-speed Eirich mixer, molded into a nozzle shape using a rubber press (molding pressure 1.0 t/d), and then fired at a temperature of 950°C in a coke Matsufuru. be. disaster"
Due to the use of raw materials, the elastic modulus is lowered and the expansion rate is also lowered.

Along with this, there is an improvement in spalling resistance. Using the material of the comparative example in Table 2 as a long nozzle, in a normally used continuous casting factory (25CyC. capacity pot, 30t
T. D. ) When the material of Example 3 was used, it was successfully used without cracking and had a conventional life of 6 Ch.
Life increased to 7~8ch.

Claims (1)

[Claims] 1 In a carbon-containing continuous casting nozzle, the main mineral phase consists of corundum and monoclinic zirconia, and the chemical composition is Al_2O_380 to 98% by weight, ZrO_22 to
A method for producing a highly corrosion-resistant continuous casting nozzle, which comprises blending 10 to 70% by weight of a refractory raw material containing 20% by weight, kneading, molding, and firing.