JPH10118749A - Nozzle for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the bottlenecking as well as the clogging of an inner hole in an economical, relatively easy and stable manner without using any mechanical method such as injection of the inert gas, without promoting the low melting point or erosion by the reaction of the aggregate in the refractory with alumina in steel. SOLUTION: In a nozzle 1, a surface layer part 2 of an inner hole has the mineral composition consisting of, by weight, 65-90% agalmatolite mainly consisting of pyrophilite (Al2 O3 .4SiO2 .H2 O), and 10-35% graphite, the binding agent is added to the mixture, and the mixture is kneaded, formed, and sintered in the non-oxidizing atmosphere. Bottlenecking as well as clogging caused by the non-metallic inclusion such as alumina can be suppressed without generating degradation of the structure of the refractory, and the stable operation can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting nozzle capable of effectively suppressing clogging of a nozzle through which molten steel passes in continuous casting of aluminum-killed steel or the like containing aluminum and further effectively suppressing blockage.

[0002]

2. Description of the Related Art A nozzle for continuous casting of molten steel is used for the following purposes.

In the continuous casting of molten steel, the nozzle for continuous casting prevents the molten steel from being oxidized by contact with the air by injecting the molten steel between the tundish molds, and also prevents the molten steel from being scattered. It is used for the purpose of preventing oxidation due to contact, preventing scattering of molten steel, and rectifying pouring of molten metal to prevent inclusion of non-metallic inclusions and floating materials on the mold surface into a slab.

Conventionally, the nozzle material for continuous casting of molten steel is mainly composed of graphite, alumina, silica, silicon carbide and the like, and recently zirconia is sometimes used as a constituent component. However, casting aluminum killed steel or the like has the following problems.

In aluminum-killed steel and the like, aluminum added as a deoxidizer reacts with oxygen present in molten steel to form α-killed steel.
Non-metallic inclusions such as alumina are formed. Therefore, when casting aluminum killed steel, etc., non-metallic inclusions such as α-alumina generated by oxidation of aluminum added as a deoxidizing agent adhere to the inner hole surface of the continuous casting nozzle, and are deposited and deposited. As a result, the inner hole is narrowed, and in the worst case, the inner hole is closed, which makes stable casting difficult. Alternatively, non-metallic inclusions such as α-alumina adhered and deposited in this manner are peeled off or fall off and are rolled up in the slab, resulting in deterioration of the quality of the slab.

In order to prevent the inner hole from being narrowed and clogged by the non-metallic inclusions such as α-alumina, the inner surface of the continuous casting nozzle for forming the inner hole is difficult to move toward the molten steel flowing through the inner hole. 2. Description of the Related Art A method of injecting an active gas to prevent non-metallic inclusions such as α-alumina present in molten steel from adhering and depositing on the inner surface of a continuous casting nozzle has been widely used.

[0007] However, the method of injecting the inert gas from the inner surface of the molten steel continuous casting nozzle forming the inner hole has the following problems.

That is, if the amount of the inert gas to be jetted is large, bubbles formed by the inert gas are caught in the slab, causing defects due to pinholes. Conversely, if the amount of the inert gas to be ejected is small, non-metallic inclusions such as α-alumina adhere to and accumulate on the inner surface of the continuous casting nozzle, and the inner hole becomes narrower and, in the worst case, clogs.

Further, it is structurally impossible to blow an inert gas uniformly from the inner surface of the continuous casting nozzle toward the molten steel flowing through the inner hole. The control of the inert gas to be ejected becomes unstable due to the deterioration of the structure and the structure of the material, and it becomes difficult to evenly eject the inert gas onto the inner surface of the continuous casting nozzle. As a result, α- Non-metallic inclusions such as alumina adhere to the inner surface of the continuous casting nozzle and accumulate to make the inner hole narrower and even clogged.

It is considered that nozzle blockage due to nonmetallic inclusions, particularly nozzle blockage due to alumina inclusions, occurs as follows.

That is, (1) aluminum in steel is oxidized by entrainment of air through a refractory joint and a refractory structure, and silica in carbon-containing refractory is digested by a reduction reaction and oxidized by supplying oxygen. And the like to produce alumina by secondary oxidation. (2) The alumina diffuses and aggregates to form alumina inclusions. (3) On the operating surface of the nozzle, carbon disappears, the surface becomes uneven, and alumina inclusions are easily deposited.

On the other hand, non-oxide raw materials (SiC, Si ₃ N ₄ , BN, ZrB ₂ , sialon, etc.) have low reactivity with aluminum oxide as a countermeasure in terms of material.
Nozzles have been proposed in which a non-oxide raw material is added to alumina-graphite or consists of itself. However, when it is added to alumina-graphite, if it is not added in a large amount, the effect of preventing adhesion is not recognized and the corrosion resistance is deteriorated, so that it is not practical. Also, when a nozzle is formed only from non-oxide-based materials, the effect can be expected, but it is not suitable for practical use due to the cost of the materials and production.

Further, an oxide raw material containing CaO (Ca
O · ZrO ₂ , CaO · SiO ₂ , 2CaO · SiO
No. ₂ ) has been proposed for the purpose of producing a low-melting substance by a reaction between CaO and Al ₂ O ₃ and dissolving it in steel, and a nozzle comprising a graphite-CaO-containing oxide raw material has been proposed. However,
The reactivity of CaO and Al ₂ O ₃ is easily affected by the temperature conditions of the molten steel during casting, and when a large amount of Al ₂ O ₃ inclusions is contained in the steel, the spalling and corrosion resistance are reduced. In some cases, a sufficient amount of CaO cannot be secured.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to form a glass layer on a nozzle operating surface during use, prevent air from being entrapped through a refractory structure, and smoothen the operating surface structure. It is economical and relatively economical without using a mechanical method such as blowing out an inert gas, and without promoting erosion to lower the melting point due to the reaction between the aggregate in the refractory and the alumina in the steel. It is an object of the present invention to provide a continuous casting nozzle that can stably narrow an inner hole and prevent clogging easily and without being affected by a change in temperature of molten steel during casting.

[0015]

According to the present invention, at least the surface layer of the inner hole in contact with molten steel has a mineral composition of pyrophyllite (Al ₂ O ₃ .4SiO ₂ .H ₂ O) as a main component. It is characterized by being made up of 90% by weight and 10% to 35% by weight of graphite, added with a binder such as an organic binder, kneaded, molded and fired in a non-oxidizing atmosphere.

[0016] In addition, the raw stone is a pyrophyllite-based natural raw material having a mineral composition which is calcined at 800 ° C. or higher to remove water of crystallization and contains 1 to 5% by weight of alkali components such as K ₂ O and Na ₂ O. use. The grain size of the rock is 250
μm or less is characterized by being 60% or less by weight of the raw stone.

The most remarkable aspect of the mineral composition of the present invention is the use of olivine. In actual use, graphite and silica coexisting with carbon are SiO ₂ (S) + C (S) = SiO (g) + CO (g) 3SiO (g) + 2A1 = 2Al ₂ O ₃ (S) + 3Si 3CO (g) + 2A1 = Al ₂ O ₃ (S) + 3C The silica is digested and decomposed by the above reaction to produce SiO (g) and CO (g), and reacts with A1 in the steel to form Al ₂ O _3, and thereby into the steel. Oxygen source. However, in the case of loasite, even in the coexistence of graphite and carbon, there is no digestion and decomposition of the particles of the loasite and SiO _{2 of} pyrophyllite (Al ₂ O ₃ .4SiO ₂ .H ₂ O), which is the main mineral of the loasite.
Is stable, make briquette consisting of rubble stone + resin powder + carbon fine powder and embed in brieze 150
Microscopic observation after heat treatment at 0 ° C. for 24 hours revealed no collapse of particles and no generation of bubbles.

The semi-melting temperature of the rock is about 1500 ° C., and the working surface in contact with the molten steel is melted to form a glass film, so that the working surface structure is smoothed and the glass film is used to pass through the refractory structure. The suppression of air entrainment is as small as 95 × 10 ⁻⁵ darcy after heat treatment at 1500 ° C. for 1 hr, whereas the air permeability is 95 × 10 ⁻⁴ darcy after heat treatment at 1000 ° C. × 1 hr. You can tell from that.

In the actual use as a nozzle for continuous casting, the mixing weight ratio of the rock is desirably 65% by weight or more in order to positively generate a glass film on the working surface, and if it is 90% by weight or more, softening deformation occurs. 90 because it grows
% By weight or less is desirable.

The compounding weight ratio of graphite is 1 in order to suppress the softening deformation of the rock and to maintain the thermal shock resistance.
The content is preferably 0% by weight or more, and if it is 35% by weight or more, the volume ratio of graphite to the rock becomes large, and tissue defects such as lamination are easily generated. In consideration of thermal conductivity and oxidation resistance, it is desirable to use natural graphite.

The reason for using the calcite that has been calcined at 800 ° C. or higher to remove the crystal water is that the crystallization water of the rock is released from 500 to
At 800 ° C., the coefficient of thermal expansion becomes abnormally large and cracks occur in the refractory.

If the average particle size of the rock is 250 μm or less and the weight ratio of the rock is 60% or more, structural defects such as lamination at the time of molding are liable to occur, and in actual use as a continuous casting nozzle. Since the softening deformation of the rock particles easily occurs, the content is preferably 60% or less.

Any of three types of rhoite can be used: pyrophyllite-type rock, kaolin-type rock, and sericite-type rock, but the working surface that comes into contact with molten steel during actual use becomes semi-molten and the glass layer Considering the formation of steel and the erosion resistance of molten steel, pyrophyllite-based rock with a fire resistance of SK29 to 32 is good. The fire resistance of kaolinite rock is SK
It is as high as 33 to 36, and conversely, in the case of sericite rock, the fire resistance is SK26 to 29, which is low.

(Action) Pyrophyllite (Al ₂ O ₃ .4)
The refractory composition consisting of 65 to 90% by weight of rocks and 10 to 35% by weight of graphite mainly composed of SiO ₂ · H ₂ O) has no digestion decomposition of the rocks even in the coexistence of graphite and carbon. It does not provide a source of oxygen into the steel, such as SiO ₂ . The semi-solid temperature of the rock is around 1500 ° C,
Form a glass coating layer on the working surface that comes in contact with molten steel,
This has the effect of smoothing the working surface structure and suppressing air entrainment through the refractory structure, thereby suppressing the adhesion of Al ₂ O ₃ and metal. Next, the nozzle for continuous casting of molten steel of the present invention will be described with reference to the drawings. FIG. 1 is an example of a schematic vertical cross section showing an embodiment of a nozzle for continuous casting of molten steel as an immersion nozzle of the present invention. The nozzle 3 for continuous casting of molten steel of the embodiment is used as an immersion nozzle disposed between a tundish and a mold. As shown in FIG. 1, in a continuous casting nozzle 3 for molten steel as an immersion nozzle having an inner hole 1 along the axis thereof through which molten steel flows, the nozzle 3 for the continuous casting of molten steel forming the inner hole 1. The inner-hole surface layer 2 is formed of a refractory having the above-described chemical composition. According to the molten steel continuous casting nozzle 3 as the immersion nozzle of the embodiment, nonmetallic inclusions such as alumina existing in the molten steel adhere to the inner surface layer 2 of the molten steel continuous casting nozzle 3 forming the inner hole 1. Suppress deposition.

Next, the present invention will be described with reference to examples.

[0026]

EXAMPLES Formulations 1 to 5 (hereinafter referred to as "samples of the present invention") having a chemical composition within the scope of the present invention shown in Table 1 and formulations 6 to 6 having a chemical composition outside the scope of the present invention. 8 (hereinafter referred to as "comparative sample"), a powder and a phenolic resin in the range of 5 to 10% by weight were added, and the mixture was kneaded and kneaded to obtain a non-alumina or other non-alumina material. 30 mm x 30 mm x 2 for testing the amount of metal inclusions and corrosion resistance to molten steel
A molded article having a dimension of φ50 mm × 20 mm for measuring a molded article having a dimension of 30 mm and a permeability, and
Form compacts having dimensions of 100 mm outer diameter, 60 mm inner diameter and 250 mm length for testing spalling resistance, and reduce each of the resulting compacts at a temperature in the range of 1000 ° C to 1200 ° C. After firing, refractories 1 to 8 were prepared.

[0027]

[Table 1]

Table 1 shows the physical property values (porosity and bulk specific gravity) of each of the above-mentioned Samples 1 to 5 of the present invention and Comparative Samples 6 to 8.

Each of the inventive samples 1 to 5 and the comparative samples 6 to 8 having the above-mentioned dimensions of 100 mm in outer diameter, 60 mm in inner diameter and 250 mm in length were heated in an electric furnace at a temperature of 1500 ° C. for 30 minutes, and After rapid cooling, spalling resistance was investigated. Table 1 shows the results.

The above-mentioned 30 mm × 30 mm × 230 mm
Samples 1 to 5 of the present invention and Comparative Samples 6 to 8 having the following dimensions were immersed in molten steel at a temperature of 1550 ° C. for 180 minutes containing aluminum in the range of 0.02 to 0.05% by weight, respectively. The erosion rate (%) and the adhesion amount of nonmetallic inclusions such as alumina were investigated. Table 1 shows the results.

Each of Samples 1 to 5 of the present invention having a size of φ50 mm × 20 and Comparative Samples 6 to 8 were heated in an electric furnace at a temperature of 1500 ° C. for 60 minutes,
After cooling, the air permeability was measured. Table 1 shows the results.

As is clear from Table 1, the sample of the present invention has excellent spalling resistance and does not adhere to nonmetallic inclusions such as alumina despite its low erosion rate. The inner hole of the nozzle is narrowed and the blockage can be effectively suppressed. In addition, since the sample of the present invention has a low air permeability, it is possible to suppress the entrapment of air through the refractory during actual use.

On the other hand, in Comparative Sample 6, although the amount of adhered alumina was small due to the high content of the rock, the spalling resistance was extremely poor and the corrosion resistance to molten steel was extremely poor. Is evident.

The sample 7 for comparison contains Al ₂ O ₃ and SiO _{2 in place} of the rock, so that Si
O ₂ oxygen remarkable amount of adhesion of alumina to supply much during digestion decomposed to steel, also, is at the comparative sample 8, instead of the roseki not contain SiO _2, only Al ₂ O ₃ Although the mineral that supplies oxygen to steel is removed, the permeability is high and non-metallic inclusions such as alumina adhere much.

[0035]

Therefore, according to the nozzle for continuous casting of molten steel of the present invention, the inner hole is narrowed by non-metallic inclusions such as alumina without deteriorating the structure of the refractory, and furthermore, the clogging is suppressed and stable operation is achieved. Can do it.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view in a case where a composition material of the present invention is provided on a surface layer of an inner hole in contact with molten steel.

FIG. 2 is a longitudinal sectional view in a case where the composition material of the present invention is provided in a surface layer portion of an inner hole and a lower portion (a molten steel immersion portion) of a molten steel continuous casting nozzle.

[Explanation of symbols]

 Reference Signs List 1 inner hole 2 inner hole surface layer 3 nozzle for continuous casting of molten steel

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 14, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

[0027]

[Table 1]

Claims (3)

[Claims] In a continuous casting nozzle, a surface portion of an inner hole in contact with molten steel has a mineral composition of pyrophyllite (A).
(1) ₂ O ₃ · 4 SiO ₂ · H ₂ O)
A nozzle for continuous casting of molten steel, which comprises 90 to 90% by weight and 10 to 35% by weight of graphite, with a binder added, kneaded, molded and fired in a non-oxidizing atmosphere. 2. The continuous casting nozzle as claimed in claim 1, wherein the pyrophyllite-based lozenge is calcined at 800 ° C. or more to remove crystallization water and contains 1 to 5% by weight of an alkali component. . 3. The limestone containing pyrophyllite as a main component has an average particle diameter of 250 μm or less, and the ration weight of the limestone is 6%.
3. The continuous casting nozzle according to claim 1, wherein the content is 0% or less.