KR950008603B1 - Composition of refractories - Google Patents

Abstract

The refractory of the dip nozzle for the continuous casting consists of 1-40 Portland cement composed of 40-90 wt% calcium zirconate clinker and 10-60 wt% graphite, 1-15 wt% wollastonite, 1-10 wt% frit. Calcium zirconate clinker includes 1.2-31.5 wt% calcium oxide and the residue of zirconia. This refractory prevents nozzle hole from decreasing or closing the hole diameter as adhering alumina is suspended in molten steel and is coated on the inside wall of the inner hole in the dipping nozzle and enhances the quality of the cast steel.

Description

Immersion nozzles for continuous casting and refractories thereof

The accompanying drawings are longitudinal sectional views showing the immersion nozzle of the present invention.

* Explanation of symbols for the main parts of the drawings

1: inner wall 2: outer wall

3: ZrO ₂ -C material 4: discharge port

The present invention relates to an immersion nozzle used in a continuous structure of steel, and in particular, that alumina suspended in molten steel adheres to the wall surface of the nozzle bore while flowing through the bore of the nozzle during molten steel so that the diameter of the nozzle bore is reduced or closed. It is related with the refractory of the immersion nozzle for continuous casting which prevents.

The immersion nozzle for molten steel casting is used between tundish and mold during continuous casting of steel to prevent slag mixing due to prevention of oxidation of molten steel and vortex prevention of molten steel to improve the quality of the cast slab. It plays a major role.

Such immersion nozzles have severe demands on thermal shock resistance, abrasion resistance, corrosion resistance, etc., under their use conditions.

Al ₂ O ₃ -C type (alumina-carbon type) is mainly used as the material that satisfies these requirements, and ZrO ₂ -C quality which is excellent in corrosion resistance is frequently used in powder line part of nozzle outer periphery where corrosion resistance is required. have.

However, in the Al ₂ O ₃ -C type immersion nozzle, aluminum added as a deoxidizer during casting of aluminum-killed steel reacts with oxygen in molten steel to generate non-metallic inclusions such as alumina, so that the alumina is immersed in the nozzle. The inner diameter of the nozzle is reduced by attaching it gradually around the inner wall surface and the discharge port portion of the nozzle, and if it is severe, the nozzle hole is completely blocked.

This clogging of the nozzle causes a reduction in casting speed and casting interruption, making it difficult to operate in a stable manner. Furthermore, when the alumina, which has been attached and deposited on the inner wall, peels and falls off and enters the cast steel, the quality of the cast is degraded.

As part of preventing the clogging of the nozzle, a method of blowing inert argon gas through the immersion nozzle inner pore wall is widely used.

However, such a case is a problem in casting for high quality cold rolled sheet steel, such that air bubbles generated by argon gas are rolled into the cast iron and defects such as pin holes are generated in the steel after the end of rolling.

In addition, during the casting of molten steel for a long time, the refractory structure deteriorates, making it difficult to stably control the amount of argon gas blown from the nozzle inner wall.

As a result, alumina adheres to the wall of the nozzle internal hole, so that the nozzle internal diameter is often reduced or clogged.

Therefore, the development of a material capable of suppressing adhesion of alumina without blowing argon gas has been studied. As an example of such a material, 10-50% by weight of graphite, 20-75% by weight of calcium oxide (CaO), and the rest is fire resistant. A CaO-C quality immersion nozzle made of aggregate is shown in Japanese Laid-Open Patent Publication No. 57-71860.

According to this, calcium oxide reacts with alumina in molten steel to produce a low melting point compound, and this low melting point compound does not adhere to the nozzle inner pore surface, and is effective in preventing nozzle clogging.

However, calcium oxide, when present alone, reacts with moisture in the air to produce calcium hydroxide (Ca (OH) ₂ ), and has great slaking ability to disintegrate tissue. Do.

Therefore, it is very difficult to actually use CaO-C immersion nozzles.

As a part of improving these problems, Japanese Laid-Open Patent Publication Nos. 62-288161 and 63-327373 disclose CaO-ZrO ₂ -Z immersion nozzles mainly composed of calcium zirconate clinker and carbon. Has been proposed.

Here, the calcium zirconate clinker is obtained by adding and melting CaO to ZrO ₂ and is composed of cubic zirconia and calcium zirconate (CaZrO ₃ ).

Therefore, CaO is suppressed from severely reacting with moisture in the air, thereby preventing the structure of the immersion nozzle from deteriorating.

In such CaO-ZrO ₂ -C immersion nozzles, calcium zirconate clinker is used as the CaO source for reaction with alumina.

That is, CaO in the calcium zirconate clinker reacts with alumina attached to the nozzle inner wall to form a low melting point compound, and the low melting point compound melts and washes off along the flow of molten steel to prevent adhesion and deposition of alumina. will be.

However, in order for the alumina attachment preventing mechanism to function properly, it is important to continuously supply a sufficient amount of CaO from the nozzle wall toward the alumina to be attached.

As can be seen from the phase equilibrium of CaO-Al ₂ O ₃ system, the melting point of 12CaO 7Al ₂ O ₃ is 1455 ℃ and the temperature of molten steel is about 1530-1560 ℃. It is possible to produce a low melting point compound, but when the supply of CaO is insufficient to produce a compound having many Al ₂ O ₃ components, the melting point of the compound is sharply increased to prevent alumina adhesion prevention effect.

In some of the CaO-ZrO ₂ -C quality nozzles actually used, alumina fractions often occur. Analysis of the immersion nozzles in this case shows that the CaO content ratio is low in the request.

In order to supply CaO sufficiently, various methods for increasing the CaO component ratio in the nozzle material have been studied. Also, even if the CaO supply is slightly insufficient, research has been conducted on a method for obtaining a low melting point compound to obtain an appropriate melting rate. .

That is, the method for increasing the CaO component ratio in the nozzle material is to increase the amount of calcium zirconate clinker and to reduce the amount of carbon.

However, if the carbon content is too small, there is a limit to the weight of the calcium zirconate clinker because the thermal shock resistance of the immersion nozzle is inferior.

Another method is to increase the CaO component in the calcium zirconate clinker.

However, in this case, too much CaO component increases the amount of free CaO remaining even after reacting with ZrO ₂ to form CaZrO ₃ , resulting in poor fire resistance and deterioration of the immersion nozzle.

Therefore, the present invention is to improve the problems in the prior art by adding calcium zirconate clinker to other raw materials that are higher in CaO component than calcium zirconate clinker and are not digestible or not very problematic.

Hereinafter, the present invention will be described.

The present invention comprises a refractory made by adding at least one selected from the following materials to a composition consisting of 4-90 parts by weight of calcium zirconate clinker and 10-60 parts by weight of graphite.

The at least one material selected here is 1-40 parts by weight of Portland cement, 1-15 parts by weight of wollastonite and 1-10 parts by weight of frit.

Among the calcium zirconate clinker 4-90 parts by weight, CaO is 1.2 to 31.5 parts by weight (the mixing ratio of CaO in the total is 3 to 35%, and when converted to parts by weight, 3% × 40 = 1.2 parts by weight, 35% 90 parts by weight = 31.5 parts by weight), and the rest is ZrO ₂ (ie, 88.8 to 8.5 parts by weight), which is melted to form a cubic ZrO ₂ and CaZrO ₃ composition.

The accompanying drawings are cross-sectional views of an immersion nozzle showing one embodiment made of a refractory material of the present invention, in which the refractory inner wall 1 made of the refractory material of the present invention and an outer wall portion surrounding the periphery of Al have excellent contents loss for molten steel. Along with the ₂ O ₃ -C material, the lower middle part consists of a respective outer wall (2) (3) made of ZrO ₂ -C material which has excellent corrosion resistance against mold powder.

And it consists of the inner hole 4 and the discharge port 5 through which molten steel flows.

The accompanying drawings are only structures showing one embodiment, and the refractory material of the present invention is not limited to the above structures.

Next, the reason for numerical limitation and the effect thereof will be explained according to the chemical component ratio of the present invention.

(1) CaO contained in calcium zirconate clinker:

CaO contained in the calcium zirconate clinker significantly reduces the digestibility of severe reaction with moisture in the air and reacts with adherent alumina to produce low melting point compounds. The more CaO content is better for the reaction with alumina, but in the present invention, since Portland cement is added as a separate CaO source, the lower limit of CaO in the calcium zirconate clinker is lowered to 3%.

However, when the CaO content ratio is 3% or less (1.2 parts by weight) or less than 3% by weight, the use of the monolithic zirconia (monoclinic zirconia) in the calcium zirconate clinker is severe and the volume change around 1000 ℃ causes a problem in safe use. do.

On the other hand, when the content ratio of CaO exceeds 35% (31.5 parts by weight), a large amount of free CaO which does not react with ZrO ₂ is present in the calcium zirconate clinker and the immersion nozzle structure is degraded.

Therefore, the CaO content in the calcium zirconate clinker should be limited to 3 to 35% (1.2 to 31.5 parts by weight).

(2) Calcium Zirconate Clinker:

Potassium zirconate clinker is used as the CaO source for reacting with adherent alumina.

When the content of the calcium zirconate clinker is 40 parts by weight or less, the amount of CaO for reacting with the adherent alumina becomes insufficient. On the other hand, when the amount of the calcium zirconate clinker exceeds 90 parts by weight, the thermal shock resistance is inferior.

Therefore, the content of calcium zirconate clinker should be in the range of 40-90 parts by weight.

(3) Graphite:

Graphite improves the thermal shock resistance by preventing the wettability of the immersion nozzle against molten steel and increasing the thermal conductivity.

When the content of graphite is less than 10 parts by weight, it is difficult to use because of poor heat shock resistance.

On the other hand, when the content of graphite exceeds 60 parts by weight, the corrosion resistance drops sharply and cannot be used for a sufficient time.

(4) Portland Cement:

Portland cement has CaO and SiO ₂ as main components and 2CaO · SiO ₂ and 3CaO · SiO _{2 as} main constituent minerals.

Since 2CaOSiO ₂ or 3CaOSiO ₂ has a melting point higher than 2000 ° C. and does not react with CaZrO ₃ , it is possible to prepare an immersion nozzle by adding portland cement to a calcium zirconate clinker.

This would alumina adheres to the inner hole wall face of the produced immersion nozzle calcium CaO component in the zirconate clinker and Portland cement is Al ₂ O ₃ reacts with the CaO-Al ₂ O ₃ based on SiO ₂ is CaO-Al containing a small amount It produces a low melting compound of the ₂ O ₃ -SiO ₂ ternary system, which may have a melting point lower than that of 12CaO.7Al ₂ O ₃ .

This addition of portland cement has the effect of increasing the content of CaO as well as broadening the range of composition in which low melting point compounds can be produced.

Therefore, when the amount of Portland cement is less than 1 part by weight, it is difficult to obtain the above-mentioned effect. If the amount exceeds 40 parts by weight, the corrosion resistance is lowered, and thus the content is not sufficient.

On the other hand, the hygroscopicity by the addition of portland cement was investigated, but there was no problem in manufacturing and storage as compared with the immersion nozzle without addition of the portland cement.

In addition, as a method of preventing the adhesion of alumina by adjusting the melting rate of the nozzle inner wall surface without increasing the CaO content in the immersion nozzle material of the present invention, the wollastonite (CaO · SiO ₂ ) or frit mentioned below are used. Can be added.

(5) Wollastonite:

The wollastonite has a melting point of 1544 ° C but due to the influence of impurities contained in the raw material, the actual melting point is about 1400 ° C, and it melts itself under the immersion nozzle use conditions to promote weakening of the matrix portion and increase the melting rate, as well as calcium zirco. It reacts with CaO in the eight clinker and turns into a 2CaO.SiO ₂ mineral to promote decomposition of the calcium zirconate clinker.

Therefore, when the content of wollastonite is less than 1 part by weight, there is no melting loss promoting effect. When the content of the wollastonite is more than 15 parts by weight, the melting loss rate becomes too large, so that the solvent resistance is poor.

(6) Frit:

Frit is vitrified by melting and cooling various raw materials such as SiO ₂ , Al ₂ O ₃ , MgO, CaO, and alkali in a predetermined ratio, and its role is basically similar to wollastonite, but it is already vitrified and therefore viscous at lower temperature. This lowers and decomposes the calcium zirconate clinker, so that the melting loss promotion effect is greater than that of wollastonite.

Therefore, when the amount of frit used is less than 1 part by weight, there is no melting loss promoting effect, and when it exceeds 10 parts by weight, corrosion resistance is remarkably lowered, making it impossible to use.

Such a wollastonite or frit is severely eroded when used in a large amount and its content is lowered, so its usage is limited.

Portland cement, wollastonite, and frits are effective even when added alone, but synergistic effect is obtained by adding at least one of them.

The following is described according to the embodiment.

In Table 1, Examples 1-8 are in the range of the present invention, and Comparative Example 2 is composed of only calcium zirconate clinker and graphite.

Comparative Example 1 is a prior art Al ₂ O ₃ -C material and Comparative Example 3-5 is to add more Portland cement and the like than the composition range of the present invention.

After adding an appropriate amount of phenolic resin to the above blending, kneading, cold hydrostatic molding at 1250 kgf / cm ² and baking in a non-oxidizing atmosphere, the quality was measured.

The results are shown in Table 1 together with the blending ratios.

In Example 1-8, all the materials are excellent in the thermal shock resistance and the corrosion resistance to molten steel, and show the alumina adhesion prevention effect.

On the other hand, in Comparative Example 2, the alumina adhesion preventing effect is not obtained stably and adhesion may occur.

In Comparative Example 1, alumina adhesion occurred a lot.

In addition, Comparative Example 3-5 has no alumina adhesion but excessive erosion by molten steel.

Table 1

* Note: 1. Thermal shock resistance was determined by the presence of cracks when water-cooled after heating to 1400 ℃ in a centrifugal furnace.

2. The molten steel erosion test and the alumina adhesion test were conducted by immersing and rotating the test piece (20 × 20 × 200mm) in the molten steel of the high frequency induction furnace while maintaining 1540 ° C × 2 hours immediately after immersion and adding aluminum every 30 minutes. Measuring the adhesion thickness was averaged five times.

Next, an experimental immersion nozzle was prepared as shown in the accompanying drawings with the material of Example 1-8.

For the purpose of comparison, the same immersion nozzle was manufactured using the material of Comparative Example 2, and the conventional immersion nozzle was prepared using the material of Comparative Example 1 to blow argon gas through the nozzle inner wall.

This nozzle was installed between the tundish and the mold, and a practical test was conducted.

As a result, all of the immersion nozzles of Example 1-8 after the fifth charge use had no alumina adhesion and the quality of the cast steel was also improved.

On the other hand, the immersion nozzle of Comparative Example 2 often had severe alumina adhesion, and the immersion nozzle of Comparative Example 1 had much alumina adhesion and poor cast quality.

Claims (3)

40-40 parts by weight of calcium zirconate clinker (ZrO ₂ .CaZrO ₃ ) and 10-60 parts by weight of graphite, 1-40 parts by weight of Portland cement, 1-15 parts by weight of wollastonite, and 1-10 parts by weight of frit. Refractory of the immersion nozzle for continuous casting which consists of one or more types selected from among them. Refractory of the immersion nozzle for continuous casting, wherein the calcium zirconate clinker 40 to 90 parts by weight of calcium zirconate (CaO) is 1.2 to 31.5 parts by weight, the remainder is the addition of ZrO ₂ . An immersion nozzle for continuous casting, wherein the refractory formed in claim 1 is installed on the inner wall of the immersion nozzle.