JPS6224846A - Nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To prevent the clogging of a nozzle and to stabilize continuous casting and to improve the quality of the steel by disposing a calcareous refractory layer formed by adding a specific ratio of an inorg. or org. compd. of a halide and alkali metal to limestone and dolomite to the inside wall of the nozzle. CONSTITUTION:>=1 Kind of the inorg. or org. compd. of a halide and alkali metal is added at 0.1-20pts.wt. to 1 or 2 kinds of the limestone and dolomite and several % water or acrylic copolymer resin is added thereto and the mixture is kneaded. The kneaded matter is coated to the inside wall of the nozzle 1 for continuous casting at 1-15mm thickness or is inserted therein after forming the kneaded matter to a pipe shape to constitute the calcareous refractory layer 3. The limestone and dolomite dissociates carbon dioxide by the heating during pouring with the nozzle 1 to form the porous active CaO layer having about 60% porosity, thereby improving the heat resistance. The CaO absorbs alumina sol to decrease the m.p. and to prevent the nozzle clogging. The continuous casting is thus stabilized and the quality of the steel is improved.

Description

[Detailed description of the invention] Industrial application field The present invention relates to a long nozzle used as a refractory for continuous casting,
Related to immersion nozzles, short nozzles, etc.

Conventional technology In recent years, cleanliness requirements have been raised for steel used in high-grade line materials, shadow mask materials for color televisions, automatic steel sheets, tinplate materials for soft drink or beer cans, marine structures, etc. are becoming stronger and stronger, and homogeneous steels with fewer surface defects or inherent defects are desired.

For this reason, efforts are being made to reduce the inclusions in steel by degassing the molten steel and absorbing or floating nonmetallic inclusions by means of dams in tanditshu. Particularly in aluminum killed steel, such as tinplate material for soft drinks or beer cans, the precipitation of Al2O3 sol in the steel often causes nozzle blockage of the continuous casting nozzle, resulting in fewer continuous castings, reduced production efficiency, and some blockages. This causes turbulence in the molten steel flow, wears out the nozzle, and increases inclusions caused by refractories. Alternatively, KAr gas is injected to prevent alumina clogging, but turbulence in the molten steel flow tends to cause surface defects and inherent defects in the steel due to entrainment of additives for continuous casting, entrainment of Ar gas, etc. However, there are various problems in producing homogeneous and clean steel. This nozzle clogging by alumina is thought to occur as follows. That is, (1) free oxygen generated as the molten steel temperature decreases reacts with aluminum in the steel, resulting in A/2o-.

The sol precipitates, (2) This 4720 sol diffuses and aggregates, causing Brownian motion.
), etc. 1203 clusters are formed, (
3) On the other hand, on the operating surface of the nozzle brick, the graphite disappears and the surface becomes uneven. (4) Near the operating surface of the nozzle brick, there is a laminar flow film with a flow rate of 50-100μ close to 0, and the molten steel and 1203 clusters adhere to the inner wall surface due to the difference in specific gravity or physical adhesion force. (5) The liquid phase of oxides < Mn, si, Ca, etc. , one layer of strong ^1203 cluster is formed, and the layer of ^1203 cluster becomes thicker in turn), resulting in nozzle blockage.

In order to prevent nozzle clogging of this type of continuous casting nozzle, Japanese Patent Laid-Open No. 56-165548 and Japanese Patent Laid-Open No. 57-38
No. 366 and Japanese Unexamined Patent Publication No. 57-56377,
A nozzle for continuous casting of lime and carbonaceous bricks has been proposed. The lime clinker of this lime/carbonaceous continuous casting nozzle reacts with the Mu1203 sol precipitated from the molten steel, resulting in C
Low melting point substances such as aO-kA205.3 Cab and AA'203 are said to have the effect of preventing nozzle clogging because they flow without stopping on the inner wall of the nozzle. Furthermore, to prevent lime clinker from being digested, metal powders such as 8t-kl, Fe, and N1, or additives such as BN and 84C are added, making it possible to prevent digestion to some extent. but,
Digestion of lime clinker cannot be inhibited by any stabilizer, and greater care must be taken in storage and use than with commonly used alumina-graphite nozzles. That is, it is difficult to sufficiently inspect the cracks in the nozzle due to the digestion of lime clinker at the site of use, and there is always the worry that the nozzle may break during use. Furthermore, in lime clinker/carbonaceous nozzles, carbon increases thermal shock resistance, but on the other hand, it has good thermal conductivity, making it easier to cool molten steel and cause Mu1205 sol to precipitate and agglomerate in molten steel.
It has the disadvantage that it is easy to cause inclusions.

Means for Solving the Problems The present invention prevents nozzle clogging of continuous casting nozzles, reduces surface defects and internal defects in steel, and improves the quality of steel.

The American inventors formed an internal layer made of limestone or dolomite on the inner surface of a continuous casting nozzle, and absorbed the sol-like alumina that precipitated from the steel or caused it to flow as a low-melting substance, thereby clogging the alumina. It was discovered that this can be prevented.

The present invention provides 100% of limestone or dolomite, one or both of them.
A refractory made by adding 0.1 to 20 parts by weight of one or more halogenated compounds, inorganic compounds of alkali metals, or organic compounds is added to the inside of the alumina/graphite nozzle where molten steel passes. A layer with a thickness of 151111 mm is formed or inserted.

FIG. 1 shows a schematic diagram of the immersion nozzle of the present invention.

The limestone or dolomite used in the present invention is not particularly limited, and may be limestone that is normally used as a raw material for lime for steelmaking or dolomite that is used as a dolomite clinker for refractories.

As for the particle size, the particle size normally used for refractories can be applied.

As the binder, a halogenated compound or an alkali metal inorganic or organic compound is used. Other compounds such as limestone and dolomite cannot be used because they cause shrinkage and peeling during preheating or steel injection. In other words, the shrinkage rate after firing of limestone and dolomite to which halogenated compounds or inorganic or organic compounds of alkali metals have been added is within the range of 0 to 2 inches, whereas when other compounds are used, the shrinkage rate is 10% or more. Shows the shrinkage rate.

This is particularly indicative of the lack of hot volumetric stability. The amount of the binder of the present invention added is 0.
1 to 20 parts by weight is desirable, and less than 0.1 parts by weight is 14 parts by weight.
If the hot bending strength at 1,400°C is less than 5 kg47cm2, the bonding strength is insufficient and it is susceptible to wear due to the flow velocity of molten steel, and if it exceeds 20 parts by weight, the hot bending strength at 1,400°C is 5 kg. /cm2 or less, which is not preferable because the bonding strength decreases. From the viewpoint of bonding strength, it is preferable that the amount of the binder of the present invention added is 3 to 10 parts by weight so that the hot bending strength at 1400 DEG C. is 30 kg/crn2 or more. Specific examples of compounds used include halogenated compounds such as sodium chloride, calcium chloride, magnesium chloride, and lithium fluoride; alkali phosphates such as sodium hexametaphosphate and potassium I phosphate; No. 3 sodium silicate; Alkali silicates such as lithium silicate, alkali borates such as borax, fluoraluminates such as sodium aluminate, alkali carbonates such as soda carbonate, or alkaline organic compounds such as sodium citrate can be used. By using one or more of these compounds ii, it is possible to ensure hot volume stability and to make adjustments such as developing hot strength.

The above calcareous refractory is kneaded with water or several grams of acrylic copolymer resin Emulnoyon.

That is, when it is difficult to obtain raw corner strength, an organic sizing agent such as acrylic copolymer resin Emulnoyon can be used instead of water.

A calcareous refractory made of such limestone or dolomite is formed on the inner surface of an alumina-graphite nozzle, or a gib-like material is inserted. The wall thickness of the calcareous refractory is preferably 1 to 15 cm. If it is less than 1 W, the insulation effect and alumina absorption effect are low and it is undesirable.
Even if it exceeds this, the effect will hardly change, the nozzle will only become thicker, and there will be no practical effect.

The continuous casting nozzle of the present invention can be stored for a long period of time without having to worry about lime digestion before use.

Normally, continuous casting nozzles are preheated before use, but at this time, the product of the present invention is sufficiently heated to 1000°C or higher to dissociate carbon dioxide gas from limestone or dolomite, resulting in a porosity of 60.
% or more of porous CaO is formed. This porous C
The thermal conductivity of the aO layer is 0.3 Kcal at +200'C
/ m, hr, 'C, which has excellent heat insulation properties, which prevents cooling of molten steel and prevents precipitation and agglomeration of Al2O3 sol. In addition, even if a single layer of active cao/m clusters is formed, the reaction product of CaO and Al2O3 has a lower melting point as the klOIJ layer increases, so even if a single layer of clusters is formed, it will easily flow out of the nozzle. Blockage is difficult to occur. Also, A/20. - Since oxidation of the graphite in the graphite nozzle can be prevented, large Al2O3 inclusions caused by oxidation of the nozzle can be reduced.

The part of the continuous casting nozzle that comes into contact with the slag or continuous casting additive may be reinforced with ZrO2 or graphite.

Examples will be described below.

Example 1 Table IK shows the quality of the Al2O3 graphite nozzle used in the present invention.

Table 2 shows the quality of the calcareous refractory that is part of the structure of the two-layer submerged nozzle of the present invention.

Products I to (1) of the present invention were obtained by carrying out lapagres at the same time as the 1203 graphite material, and reducing and firing at 800° CK. In addition, the products ① and ② of the present invention are made by turning the completed Al2O3/graphite nozzle.
This is a cylindrical piece of unfired calcareous refractory that has been pre-formed with wrapper braces. The molding pressure was 1 ton/α2 in both cases.

Table I Quality of Al2O5-Graphite Nozzle Table 2 Quality of Calcareous Refractory Layer Example 2 The immersion nozzle of the present invention shown in Table 2 was used in a 35-ton tundish made by Lambda. The steel type is aluminum killed steel,
A comparison was made with a conventional Al2O5/graphite immersion nozzle. The immersion nozzle of the present invention, which has a calcareous refractory interior, does not blow argon gas and is similar to the conventional A720.
．．・Graphite immersion nozzle uses st7 minute argon.
I blew gas. As a result, the product of the present invention /203
There was almost no adhesion, and both the surface defect rate and the number of nonmetallic inclusions of the steel pieces were low, showing good properties. The results are shown in Table 3. Effects of the Invention As described above, the continuous casting nozzle of the present invention exhibits excellent heat insulation properties, At203 absorption properties, etc., and as a result, there is no nozzle clogging due to adhesion of Al2O sol, and the nozzle is stable. As the plant became operational, the quality of the steel also improved.

The following effects of the present invention can be summarized as follows.

1) The calcareous inner layer of the present invention can be easily treated as a salt9 without any worries about digestion until the point of use. 2) By preheating during use, it forms a porous heat insulating layer with an apparent porosity of around 60 cm, which cools the molten steel. This prevents alumina sol from forming and coagulating.

3) After preheating, it becomes active CaO and can absorb alumina in steel. Alternatively, a low-melt material can be formed and flowed out without remaining on the inner wall of the nozzle.

4) Oxidation of the alumina-graphite nozzle can be prevented, and large inclusions caused by the nozzle can be prevented.

[Brief explanation of the drawing]

Figures 1 to 5 are vertical cross-sectional views of the nozzles 1 to V shown in Table 3, which are examples of the nozzle of the present invention, and Figure 6 is a vertical cross-sectional view of another example of the nozzle of the present invention. , 1 in the figure is N120
3.Graphite refractory; 2 indicates ZrO2 graphite refractory; 3 indicates a calcareous refractory layer.

Claims (2)

[Claims] (1) A calcareous refractory made by adding 0.1 to 20 parts by weight of one or more halogenated compounds or alkali metal inorganic or organic compounds to 100 parts by weight of one or both of limestone or dolomite. A continuous casting nozzle characterized in that a layer having a thickness of 1 to 15 mm is disposed inside a molten steel discharge port of the continuous casting nozzle. (2) Continuous casting according to claim 1, wherein the calcareous refractory layer disposed inside the molten steel outlet is simultaneously formed, or the inner side of the molten steel outlet is inserted and disposed after turning. Nozzle for.