JPH08215810A - Nozzle for continuously casting molten steel - Google Patents

Abstract

PURPOSE: To economically obviate the generation of the constriction and closure of an inside hole and the deterioration of structures over a long period of time without using a mechanical method, such as ejecting of inert gas. CONSTITUTION: The surface layer part of an inside hole 1 in contact with molten steel consists of 40 to 65wt.% calcium zirconate essentially consisting of CaO.ZrO2 as an ore compsn., 10 to 35wt.% graphite, 1 to 25wt.% in total of calcium silicate essentially consisting of CaO.SiO2 and crystalline stabilized calcium silicate consisting essentially of 2CaO.SiO2 or 3CaO.SiO2 which are used in combination and 5 to 25wt.% zircon clinker consisting essentially of ZrO2 .SiO2 . This nozzle 3 for continuous casting is formed by adding an org. binder to the compsn. described above, kneading and molding the mixture and firing the molding in a nonoxidizing atmosphere. As a result, the constriction and closure of the inside hole by nonmetallic inclusions, such as α-alumina, are suppressed stably over a long period of time.

Description

Detailed Description of the Invention

[0001]

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

[0002]

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

In continuous casting of molten steel, the nozzle for continuous casting prevents molten steel from oxidizing due to contact with air by injecting molten steel between tundish molds, and prevents scattering of molten steel, and further, non-metallic inclusions and molds. It is used for the purpose of rectifying the pouring of molten metal in order to prevent the surface suspended matter from getting caught in the slab.

Conventionally, the nozzle material for continuous casting of molten steel is mainly composed of graphite, alumina, silica, silicon carbide, etc., and recently, zirconia may be used as a constituent component. However, there are the following problems when casting aluminum killed steel and the like.

Aluminum-killed steel and the like have α-reacted with aluminum added as a deoxidizer by reacting with oxygen present in molten steel.
Non-metallic inclusions such as alumina are produced. Therefore, when casting aluminum-killed steel or the like, non-metallic inclusions such as α-alumina generated by the oxidation of aluminum added as a deoxidizing agent adhere to the inner hole surface of the nozzle for continuous casting, and are 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 way are peeled off or fallen off and are entrapped in the slab, resulting in deterioration of the quality of the slab.

In order to prevent the narrowing and blockage of the inner hole due to the non-metallic inclusions such as α-alumina, the inner surface of the continuous casting nozzle forming the inner hole faces the molten steel flowing through the inner hole. A method is widely used in which an active gas is injected to prevent non-metallic inclusions such as α-alumina existing in molten steel from adhering to and depositing on the inner surface of the nozzle for continuous casting.

However, the method of ejecting the inert gas from the inner surface of the molten steel continuous casting nozzle forming the above-mentioned inner hole has the following problems.

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

Further, it is structurally impossible to uniformly blow the inert gas from the inner surface of the continuous casting nozzle toward the molten steel flowing through the inner hole, and when casting for a long time, the continuous casting nozzle is required. With the deterioration of the structure and the structure of the material, the control of the inert gas to be jetted becomes unstable, and it becomes difficult to jet the inert gas uniformly to the inner surface of the nozzle for continuous casting, resulting in α- Non-metallic inclusions such as alumina adhere to the inner hole surface of the continuous casting nozzle and are deposited to narrow the inner hole and further block it.

[0010]

Therefore, in order to solve the above-mentioned problems without using mechanical means such as jetting of an inert gas, the following method is used as a material countermeasure for the nozzle for continuous casting of molten steel. Was used.

The following molten steel continuous casting nozzle containing graphite and calcia as main components is disclosed in JP-A-57-71860. That is, it is a nozzle for continuous casting of molten steel, which is essentially made of a refractory material consisting of:

10 to 50 wt% graphite and 20 calcia
˜75% by weight and the balance is made of metallic aluminum, silicon carbide or the like.

However, the above molten steel continuous casting nozzle has the following problems. Calcia rapidly reacts with non-metallic inclusions such as α-alumina to form low melting point compounds.
As a result, it has an effect of preventing non-metallic inclusions such as α-alumina from adhering to and depositing on the surface of the inner hole of the continuous casting nozzle. However, if calcia is present alone, it reacts violently with water or moisture in the air even at room temperature to form Ca (OH) ₂ , which disintegrates and powders, so special care is required when manufacturing nozzles, and moisture-proof treatment is required. It cannot be used without applying. Further, since calcia has a large coefficient of thermal expansion, when it is heated so that an uneven temperature distribution is generated, a large thermal stress is generated inside the nozzle, and the heat-resistant sprinkling property is greatly reduced.

Due to the above-mentioned problems, it is difficult to practically use a continuous casting nozzle containing calcia alone.

Further, JP-A-64-40154 discloses graphite-calcium zirconate. In this method, Al ₂ O _{3 as} an adhering substance and CaO coming from calcium zirconate are reacted with each other to be converted into a low-melting compound so as to be lost. [CaO 23% (40 mol%)
~ 36% (55 mol%) Containing Calcium Zirconate]
CaO.ZrO ₂ decomposes when it comes into contact with alumina at the temperature of molten steel and releases CaO (see Japanese Patent Publication No. 59-19075). However, depending on casting conditions, the release rate is slow and it functions sufficiently. It turns out that there are cases where it does not.

Release of CaO / ZrO ₂ by decomposition
Silica (Si
It is effective to add O ₂ ), magnesia (MgO), etc.
It is disclosed in Japanese Examined Patent Publication No. 3-14540.

[0017] CaO, CaO-SiO ₂ having both properties as means and CaO component extender to facilitate movement aggregation into release-surface of CaO by the decomposition of ZrO ₂ (CaO40
Up to 54%) is effective.
No. 9 is disclosed.

[0018] CaO-SiO ₂ having both properties as means and CaO component extender to facilitate movement aggregation into release-surface of CaO by decomposition of CaO-ZrO _2, 2CaO ·
The combined addition of SiO ₂ and 3CaO.SiO ₂ (the total amount of which is 1 to 35% by weight) is effective, and is disclosed in JP-A-4-73409.
And Japanese Patent Application Laid-Open No. 4-73410.

In the case of, CaO.ZrO ₂ and Ca
_{O · SiO 2, 2CaO · SiO} 2, 3CaO · SiO 2 (1~
(35%), the surface texture after reacting with Al ₂ O ₃ to form low melting point minerals becomes uneven, and non-metallic inclusions accumulate and accumulate in the recesses, making it difficult to use for a long time. It becomes, especially if there are many α-Al ₂ O ₃ in the steel α-Al ₂ O ₃
Are rapidly deposited and are difficult to use.

From the above, a continuous molten steel for preventing the inner hole from narrowing and clogging for a long time economically and relatively easily without using a mechanical method such as jetting an inert gas. Although there is a strong demand for the development of a casting nozzle, such a molten steel continuous casting nozzle has not been proposed yet.

[0021]

The present invention has been made to solve the above problems, and an object of the present invention is economical without using a mechanical method such as jetting an inert gas. The object is to provide a nozzle for continuous casting of molten steel, which has a narrow inner hole and does not cause blockage or deterioration of the structure for a long time.

The present invention is formed of a refractory material consisting essentially of:
It is arranged in one part of the inner hole.

As a mineral composition, 40 to 65% by weight of calcium zirconate containing CaO.ZrO ₂ as a main component and graphite 1
0 to 35% by weight, as a mineral composition CaO / SiO ₂ as a main component calcium silicate and as a mineral composition 2Ca
O-SiO ₂ and 3CaO-SiO ₂ are mainly used as the crystal-stabilized calcium silicate, and the total is 1
-25% by weight, 5 to 25% by weight of zircon clinker containing ZrO ₂ · SiO ₂ as a main component as a mineral composition.

The nozzle for continuous casting of molten steel composed of the above refractory material suppresses the viscous reaction of its component, calcia (CaO), with water or water in the air.
Calcium silicate mainly composed of O ₂ and 2CaO ・ S
Both of the crystal-stabilized calcium silicate containing TiO ₂ and 3CaO · SiO ₂ as a main component have no crystal transformation with respect to temperature change, so that there is no abnormal expansion and contraction, so that the structure of the nozzle is prevented from deteriorating and a nozzle for continuous casting of molten steel is provided. Aluminum added as a deoxidizing agent on the surface of the inner hole reacts with oxygen present in the molten steel to form a low melting point compound by reacting with a non-metallic inclusion such as α-alumina, It is possible to prevent non-metallic inclusions such as α-alumina from adhering to and further depositing on the surface of the inner hole of the molten continuous casting nozzle.

Regarding the principle and effect of the material, it is obvious that the use of a stable, high CaO-containing substance that is not digestible is the key point for achieving the effect, and various raw materials (minerals) were examined. As a result, calcium silicate containing CaO · SiO ₂ as a main component and 2CaO · SiO ₂ as a CaO release accelerator by decomposition of calcium silicate.
It was found that both the crystal-stabilized calcium silicate containing 3CaO.SiO ₂ as a main component are effective. This substance reacts with α-Al ₂ O ₃ as a main component of non-metallic inclusions to further lower the melting point by using a SiO ₂ source as a release accelerator and a CaO component extender, or by using both together. It can be measured.

The CaO component reacts with Al ₂ O ₃ to form CaO.A.
l ₂ O ₃ , 3CaO · Al ₂ O ₃ , finally 12CaO · 7
It becomes a low melting point substance below the melting temperature such as Al ₂ O _{3 and} is melted away, so that it is effective in preventing clogging without depositing.

More specifically, CaO is used as a mineral composition.
・ Calcium zirconate containing ZrO ₂ as a main component is C
aO is contained in the range of less than 36% by weight at the maximum, 1600 ° C
It was melted and adjusted at the above high temperature. It has the same thermal expansion properties as stabilized zirconia, and because calcia does not exist alone, it does not react violently with water or water in the air and prevents nozzle tissue degradation.

The above-mentioned calcium zirconate in the range of 40 to 89% by weight is calcium silicate whose main component is CaO.SiO ₂ and 2CaO.SiO ₂ and 3CaO.
When coexisting with a crystal-stabilized calcium silicate containing SiO ₂ as a main component, calcia (CaO) solid-dissolved in calcium zirconate easily moves to the surface of calcium zirconate particles. CaO SiO _{2 CaO · SiO 2 48.3% 51.7%} 2CaO · SiO 2 65.1% 34.9% 3CaO · SiO 2 73.7% 26.3%

That is, calcia (CaO) for reacting with α-Al ₂ O ₃ which is the main component of the non-metallic inclusions adhering to the surface of the inner pores moves to the surface of the calcium zirconate particles.
Aggregate to increase the calcia (CaO) concentration at the grain boundary. Also, by using each calcium silicate together,
The silica (SiO ₂ ) component in calcium silicate is α-
It exerts a catalytic function to promote the reaction between Al ₂ O ₃ and calcia (CaO).

With respect to each of the above-mentioned calcium silicates, first, the calcium silicate containing CaO.SiO ₂ as a main component does not cause a hydration reaction if a mineral having a molar ratio of CaO and SiO ₂ of 1: 1 does not occur. Crystal transformation due to ascent does not occur. Also 2CaO ・ SiO ₂ and 3CaO ・ Si
The crystal-stabilized calcium silicate containing O ₂ as a main component has a molar ratio of CaO to SiO ₂ of ₂ to 3: 1 and is synthesized with 1 to 5% by weight of B ₂ O ₃ having a function of a crystal stabilizer. In the case of the other, no hydration reaction occurs, and the crystal transformation to the γ phase due to the temperature rise does not occur, so that the structure deterioration of the nozzle does not occur.

The calcium silicate containing CaO.SiO ₂ as the main component is preferably 40 to 54% by weight of CaO.
The crystal-stabilized calcium silicate mainly composed of CaO · SiO ₂ and 3CaO · SiO ₂ is 62 to 73% by weight of CaO.
It is preferable to contain

Further, as a result of various studies as means for smoothing the surface properties of the operating surface, zircon ultrafine powder as an additive having functions of facilitating decomposition / release of CaO / ZrO ₂ and migration / aggregation to the grain surface The addition proved to be effective.

That is, the zircon clinker containing ZrO ₂ .SiO ₂ as the main component as the mineral composition is preferably 5 to 25% by weight, and the average particle size of the zircon clinker is 6 μm or less in order to have good surface smoothness. Is desirable.

From the above, the disadvantages of calcia are overcome and the reaction between calcia and α-alumina is continued for a long time to form a low melting point compound, and thus the non-metallic inclusions such as α-alumina are transferred to the inner pore surface. The present invention provides a nozzle for continuous casting of molten steel capable of effectively suppressing the adherence of molten steel for a long time.

Note that SiC may be added for the purpose of improving spalling resistance and oxidation resistance.

[0036]

The content of the zirconia clinker containing CaO.ZrO ₂ as a main component as the mineral composition is preferably 40 to 65% by weight. If the content is less than 40% by weight, the calcia content necessary for reacting with α-alumina, which is the main component of the non-metallic inclusions, is poor and the corrosion resistance to molten steel is poor, resulting in a nozzle hole as shown in FIG. When it is arranged on the surface layer, that part may disappear in a short time, and a sufficient effect cannot be expected.

If it exceeds 65% by weight, the coefficient of thermal expansion becomes high and the spalling resistance is deteriorated. Graphite content is 1
0-35% by weight is desirable, and in consideration of thermal conductivity and oxidation resistance, it is desirable to use natural graphite. If the graphite content is less than 10% by weight, the heat spalling resistance is poor, while if it exceeds 35% by weight, the corrosion resistance is reduced.

The maximum content of CaO in the calcium silicate containing CaO.SiO ₂ as the main component is 54.
If the content is more than 0.5% by weight, the mineral composition becomes unstable if the content is more than that, and the hydration reaction of calcia (CaO) is likely to occur, which may cause deterioration of the structure. Further, CaO content in the crystal stabilized calcium silicate as a main component 2CaO · SiO ₂ and 3CaO · SiO ₂ as the mineral composition 62-73 wt%, SiO ₂ content of 26 to 34 wt%, and stable crystalline The content of the agent B ₂ O ₃ is in the range of 1 to 5% by weight, and the total of the three is preferably 95% by weight or more, and otherwise the crystal transformation to the γ phase is likely to occur. Further, the hydration reaction of calcia (CaO) is likely to occur, which may cause deterioration of the tissue.

Both of the above calcium silicates are used in combination, and the total content is preferably 1 to 25% by weight.

The content of both calcium silicates is 1
If it is less than 25% by weight, the effect of migrating and aggregating calcia (CaO) in calcium zirconate to the particle surface cannot be obtained, and if it exceeds 25% by weight, the structure of the refractory material is likely to deteriorate and the corrosion resistance decreases. At the same time, the heat resistance of the spall is greatly reduced.

The average particle size of the zircon clinker having ZrO ₂ .SiO ₂ as a main component as a mineral composition is 6 μm or less,
The content is preferably 5 to 25% by weight. Not obtained the effect of the content of zircon is moved aggregation calcia in the zirconia clinker is less than 5% by weight on the particle surface, 25% by weight, CaO · ZrO _2, absolute loss of CaO · SiO ₂ Due to (CaO reduction), reactivity with α-Al ₂ O ₃ is poor, low-melting point mineral is poorly produced, non-metallic inclusions such as Al ₂ O ₃ are attached, and nozzle clogging progresses. If the average particle size of the zircon clinker is 6 μm or less, the refractory has a smooth surface and the surface area is large, so that CaO / Zr
It has the effect of facilitating and promoting the decomposition / release of O ₂ and the movement / aggregation to the grain surface. Next, the molten steel continuous casting nozzle of the present invention will be described with reference to the drawings.

FIG. 1 is an example of a schematic vertical section showing an embodiment of a nozzle for continuous casting of molten steel as the immersion nozzle of the present invention. The molten steel continuous casting nozzle 3 of the embodiment is used as an immersion nozzle arranged between a tundish and a mold. In a molten steel continuous casting nozzle 3 as an immersion nozzle having an inner hole 1 through which molten steel flows as shown in FIG. 1 along its axis, the molten steel continuous casting nozzle 3 forming the inner hole 1 The part 2 is formed of a refractory material having the above-described chemical composition. According to the molten steel continuous casting nozzle 3 as the immersion nozzle of the embodiment, the molten steel continuous casting nozzle 3 forming the inner hole 1 is formed.
Adhesion and deposition of non-metallic inclusions such as α-alumina existing in the molten steel on the part 2 of 1 are suppressed for a long time.

[0043]

The effects of the present invention will be described below with reference to examples.

[0044]

EXAMPLES Formulations 1 to 5 (hereinafter referred to as “samples of the invention”) having chemical composition within the scope of the present invention shown in Table 1 and formulations 6 having chemical composition outside the scope of the present invention To each of 10 (hereinafter referred to as "comparative sample"), powder and solution phenol resin in the range of 5 to 10% by weight was added, and the mixture was kneaded and kneaded to obtain a raw material kneaded clay. 30mm x 30mm for testing the amount of non-metallic inclusions and corrosion resistance to solution
A molding having a dimension of 230 mm and a molding having an outer diameter of 100 mm, an inner diameter of 60 mm and a length of 250 mm for testing spalling resistance are formed and each of the resulting moldings is from 1000 ° C to 1200 ° C. Refractory materials 1 to 10 were prepared by reduction firing at a temperature within the range.

[0045]

[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 10.

Then, the above-mentioned outer diameter 100 mm and inner diameter 60
Inventive Samples 1 to 5 and Comparative Samples 6 to 10 each having dimensions of mm and a length of 250 mm were heated in an electric furnace at a temperature of 1500 ° C. for 30 minutes and quenched with water to investigate spalling resistance. . Table 1 shows the results.

Then, the above-mentioned 30 mm × 30 mm × 23
Inventive Samples 1 to 5 and Comparative Samples 6 to 10 having dimensions of 0 mm 0.03 to 0.05 respectively
1550 ° C., containing aluminum in the weight% range
It was immersed in molten steel at the temperature of 180 minutes for 180 minutes to examine the melting loss rate (%) and the amount of non-metallic inclusions such as α-alumina attached.
Table 1 shows the results.

As is clear from Table 1, the samples of the present invention are excellent in spalling resistance, and non-metallic inclusions such as α-alumina do not adhere even though the melting loss rate is low.
Therefore, the inner hole of the molten steel continuous casting nozzle can be narrowed and the clogging can be effectively suppressed.

On the other hand, in sample 6 for comparison, the spalling resistance is remarkably inferior due to the high content of zirconia clinker, and due to the absence of calcium silicate, α-alumina and the like are contained. It is clear that the amount of non-metallic inclusions is large.

Further, in Comparative Sample 7, the corrosion resistance to molten steel was remarkably poor due to the high content of calcium silicate, and in Comparative Sample 8, the high graphite content was caused. Sample 7 for comparison
It is obvious that the corrosion resistance to molten steel is remarkably inferior similarly to.

Therefore, according to the nozzle for continuous casting of molten steel of the present invention, the structure of the refractory is not deteriorated, the inner hole is narrowed by the nonmetallic inclusions such as α-alumina, and the clogging is stably suppressed for a long time. can do.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view in the case where a composition material of the present invention is provided in a surface layer portion of an inner hole which contacts molten steel.

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

[Explanation of symbols]

 1 Inner hole 2 Part 3 Nozzle for continuous casting of molten steel

Claims (2)

[Claims] 1. A least inner hole surface layer portion of calcium zirconate 40-65 wt% of a main component CaO · ZrO ₂ as mineral composition in contact with molten steel, 10 to 35 wt% graphite, CaO · SiO ₂ as a mineral composition Calcium silicate containing as main component and 2CaO ・ SiO ₂ as mineral composition
Or 3CaO · SiO ₂ as a main component and a crystal-stabilized calcium silicate are used together, the total amount is 1 to 25% by weight, and the mineral composition is 5 to 25% by weight of a zircon clinker containing ZrO ₂ · SiO ₂ as a main component. A nozzle for continuous casting of molten steel, characterized by comprising an organic binder, kneading, shaping, and firing in a non-oxidizing atmosphere. 2. The crystal-stabilized calcium silicate is Ca
O in the range of 62 to 73% by weight, SiO _{2 in the} range of 26 to 34% by weight, and stabilizer B ₂ O _{3 in} the range of 1 to 5% by weight, the total of these three is 95% by weight or more, and the mineral composition is ZrO ₂ .SiO ₂ The nozzle for continuous casting of molten steel according to claim 1, wherein the zircon clinker containing as a main component has an average particle size of 6 μm or less.