JPH0437453A - Nozzle for casting wide and thin slab - Google Patents

Abstract

PURPOSE:To provide a nozzle having excellent durability by incorporating zirconia, calcium zirconate stabilized with CaO, kneading and forming blending material containing refractory raw material of Al2O3, etc., and mosophase carbon, etc., and burning under non-oxidizing atmosphere. CONSTITUTION:The blending material containing 30-70 wt% the zirconia and calcium zirconate stabilized with CaO, 5-30 wt% the refractory raw material having <= 50mum particle diameter and composed of mullite, baddelegite and corundum and 25-85 wt% Al2O3, 10-70 wt% ZrO2 and 5-25% SiO2, 3-15 wt% the mesophase carbon having <= 50mum particle diameter, 3-10 wt% metallic silicon and 5-40 wt% graphite, is kneaded and formed by using bonding material. Then, after drying, this is burnt under non-oxidizing atmosphere to manufacture the nozzle. By this method, the nozzle having excellent cool of elasticity and spalling resistance can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a casting nozzle used for wide slab casting that has high hot strength and prevents alumina deposition.

[Prior Art] Casting nozzles used for casting wide, thin-walled slabs have a complex structure, and the entire nozzle is exposed to high-temperature molten steel and is constantly subjected to mechanical or thermal shocks. Because of the risk of cracking, the nozzle is required to be made of a material that has particularly high thermal strength and excellent spalling properties.

Methods for improving mechanical strength include adding a large amount of resin used as a binder, adding ultra-differential aggregate with small particle size to make the structure dense, and adding metals such as AE and Si. A method of adding metal to develop metal-based bonds in the firing process of refractories, increasing the molding pressure of refractories,
Methods for making the organization more precise are being developed.

Furthermore, in the immersion nozzle, A precipitated from the molten steel.
Nozzle hole clogging due to adhesion of oxidation products such as l21ts is a bottleneck in durability, and conventional methods have been to blow gas such as argon gas, or to use cylinders made of zirconia stabilized with CaO, calcium zirconate, and graphite. A shaped nozzle has been developed.

[Problem to be solved by the invention] However, when the strength is improved by such a method,
There is a problem in that the elastic modulus of the material increases to the same extent as or more than the improvement in strength.An increase in the zero elastic modulus means a decrease in durable poling property. In a nozzle for casting wide, thin-walled slabs, high strength and resistance to thermal shock are important, and sacrificing durable poling properties in order to increase strength is undesirable in actual use.

A again! Even in the method of preventing the adhesion of 20B, blowing argon gas has not been able to completely remove the alumina adhesion, and the above-mentioned nozzle also has low mechanical strength and cannot be used for casting wide thin-walled slabs. .

In order to apply a cylindrical nozzle made of CaO-stabilized zirconia and calcium zirconate and graphite, which are excellent in preventing Aβ203 adhesion, to a nozzle for casting wide thin-walled slabs, the elastic modulus of the material can be improved by improving the strength using conventional methods. increases to the same extent as or more than the increase in strength, and the durable pollability decreases. A nozzle for casting wide thin slabs requires high strength and spalling resistance.

The present invention has been made in view of these problems, and provides a nozzle for casting wide thin-walled slabs that has high hot strength and is excellent in preventing adhesion of alumina and the like.

[Means for Solving the Problems] The present invention for solving the problems described above uses 30 to 70% by weight of one or both of CaO-stabilized zirconia and calcium zirconate, and the particle diameter is 50 μm or less. The mineral phase consists of mullite, baddellite, and corundum, and contains 25 to 85% by weight of AβtOs, Zr(blO
-70% by weight, 5-30% by weight of a refractory raw material (hereinafter abbreviated as ZRM) having a chemical composition of 0.5-25% by weight of Si, and 3-15% by weight of mesophase carbon with a particle diameter of 50LLm or less. , wide thin slab casting characterized by kneading and molding a compound containing 3 to 10% by weight of metallic silicon and 5 to 40% of graphite using a binder, drying and firing in a non-oxidizing atmosphere. This is a nozzle for

[Function] In the present invention, 30 to 70% by weight of one or two of zirconia and calcium zirconate stabilized with CaO is used to prevent adhesion of Ag, IO, and to improve strength.
If the content is less than 630% by weight, the adhesion prevention effect will not be sufficient, and if it exceeds 70% by weight, the content of graphite and mesophase carbon will decrease, resulting in a decrease in spalling resistance.

Note that the particle diameter is preferably 80 μm or less.

Next, the particle diameter is 50 um or less, the main mineral phase consists of mullite, baddellite, and corundum, and Al22
0.25-85% by weight, ZrOi 10-70% by weight,
ZRM with a chemical composition of 25% by weight of SiO
Contains 0% by weight. The coefficient of thermal expansion of this raw material from room temperature to 1000℃ is 7 x 10-'/”C, 1000~1
The coefficient of thermal expansion at 600° C. is 2 to 4 × 10 −′/° C., and the thermal expansion is particularly small at high temperatures, and the durable poling property is excellent. If the ZrL content is less than 100% by weight, the amount of zirconia precipitated inside or around the mullite or corundum crystal is small, resulting in poor corrosion resistance, and if it exceeds 70% by weight, ZrO□ exists in a monoclinic system, resulting in abnormal expansion. There is a hailstorm, and the durability of polling is poor.

The content of this ZRM in the blended raw materials is defined as 5 to 30% by weight. If it is less than 5% by weight, sufficient effects cannot be obtained;
When it exceeds 30% by weight, it reacts with CaO in CaO-stabilized zirconia and calcium zirconate to produce a low-melting substance, resulting in a decrease in strength. In addition, the particle size is determined by measuring the particle diameter by 50
Very high strength can be obtained by setting the thickness to .mu.m or less.

Next, regarding mesophase carbon, when petroleum-based or coal-based pitch is heated, free carbon and hydrocarbons aggregate with a certain blending property, producing a liquid crystal with optical anisotropy. This is a sphere with a size of several micrometers to several tens of micrometers, which is called a micromembrane phase. When this is further heated, the microscopic spheres coalesce to form a mass called bulk mesophase. Furthermore, bulk mesophase is carbonized and becomes coke, and the present inventors focused on the fact that a strong bonding effect is developed during the process of micromesophase coalescing into bulk mesophase. An attempt was made to use it as a strength imparting agent.

As a result, it was found that Micromenphase is effective in improving strength, and at the same time, it is possible to prevent a decrease in spalling resistance by suppressing an increase in elastic modulus.

Mesophase carbon exhibits a strong bonding effect due to the coalescence of memphas spheres and the void filling effect due to softening and melting due to heating during firing of refractories, forming strong carbon bonds. This carbon bond is a pitch-derived soft carbon bond, which causes little increase in elastic modulus and is effective in improving spalling resistance.

It is necessary to use mesophase carbon that has not yet coalesced into bulk mesophase by heating. For this purpose, the heat treatment temperature needs to be 300 to 500°C, and in order to define the stage before the coalescence of the memphas progresses and the sphere size increases,
The sphere size was 50 μm or less. If the heat treatment is excessive, the mesophase spheres will coalesce, and the binding effect will not be sufficiently exerted when used in refractories.

On the other hand, if the memphis content is insufficient due to insufficient mesophasing, the volatile content due to pitch will increase, forming pores when firing the refractory and weakening the structure. The amount needs to be 50% by weight or more, and the volatile content needs to be 30% by weight or less.

Mesophase carbon, which has the effect of improving strength and suppressing the increase in elastic modulus, does not have a sufficient effect when used in less than 3% by weight, and if used in excess, carbon's inherent low wear resistance may be reduced. , there are problems such as dissolution into molten steel,
Moreover, if the amount exceeds 15% by weight, the strength decreases, so the amount used is 3 to 15% by weight, and the particle diameter is 50 μm or less.

Further, for the purpose of improving strength, it contains 3 to 10% by weight of metallic silicon. If it is less than 3%, the effect will be small, and if it is more than 10%, the spalling resistance will decrease.

Graphite includes natural scaly graphite and raw graphite.

Artificial graphite obtained by heat treating coke or the like can be used, but flaky graphite is preferable from the viewpoint of corrosion resistance and durable poling.If the graphite content is less than 5% by weight, the slag resistance of graphite will not be exhibited; If it exceeds % by weight, high strength cannot be obtained and the resistance to molten steel deteriorates.

In addition, it is preferable that the maximum particle diameter of the aggregate to be mixed is kept to 50 μm in order to improve the strength.

[Example] The present invention will be explained based on examples.

The blended refractory raw materials shown in Tables 1 to 3 were mixed using a phenol resin as a binder, and after molding, reduction firing was performed to obtain a nozzle for casting a wide thin slab. Note that Table 1 mainly shows C.
Table 2 shows the results of testing properties such as strength based on changes in the particle diameter of aO and ZrO and the amount of metal silicon; Table 2 shows changes in the amount of ZRM added; Table 3 shows the results of testing properties such as strength based on changes in the amount of mesophase carbon.

Table (weight%) Table (weight%) No in Tables 1 to 3, 1 to 3.8 to 11.15 to 1
9 is an example, 4 to 7, 12 to 14, and 20 to 22 are comparative examples.

In Example No. 1.2, the maximum particle diameters of CaO.ZrO□ (calcium zirconate) were set to 80 μm and 50 μm, and the strength was high and the spalling resistance was good. Also, No. 3 contains 10% by weight of metal silicon.
It has even higher strength. Comparative example No.
, 4.5 has a large maximum particle diameter of the calcium zirconate and has low strength, Comparative Example No. 6 has a lower amount of metal silicon than the claimed range and has low strength, and Comparative Example N
No. 7 exceeds the scope of this claim, and although the strength is high, the durable poling property is poor.

In Examples Nos. 4 to 7, the amount of ZRM was varied from 5 to 30% by weight, and they had high strength and excellent spalling resistance. On the other hand, the comparative fall 12.13 is ZRM
In Comparative Example No. 14, the amount of ZRM exceeds the claimed range and the strength is low.

Examples Nos. 15 to 17 are those in which the amount of mesophase carbon is changed from 3 to 15% by weight, and Example 18.19
are respectively CaO-stabilized Zr02j! and cao・Zr
0- (calcium zirconate) is used alone, and both have high strength and excellent spalling resistance. Comparative example No. 20.21 has a lower amount of mesophase carbon than the claimed range, and has poor spalling resistance.
Comparatively, No. 22 has a mesophase carbon content exceeding the claimed range and has low strength.

〔Effect of the invention〕

As explained above, the casting nozzle according to the present invention prevents the adhesion of oxidation products such as CaO
It prevents adhesion by containing silconi-calcium zirconate stabilized with silconium zirconate, and has higher hot strength than conventional nozzles, as well as excellent elastic modulus and durable poling properties. Moreover, it is highly resistant to hole clogging and has excellent durability as a nozzle for casting wide, thin-walled slabs that are subjected to mechanical or thermal shocks such as internal and external pressures of molten steel.

Claims (1)

[Claims] 30-70% by weight of one or two of zirconia and calcium zirconate stabilized with CaO, particle diameter is 50 μm or less, mineral phase consists of mullite, baddellite, corundum, Al_2O_325-85% by weight, ZrO_210-70 Weight%, SiO_25~25
5-30% by weight of refractory raw materials with a chemical composition of 5% to 30% by weight
A mixture containing 3 to 15% by weight of mesophase carbon with a particle diameter of 50 μm or less, 3 to 10% by weight of metallic silicon, and 5 to 40% of graphite is kneaded and molded using a binder, and after drying, it is A nozzle for casting wide, thin-walled slabs that is produced by firing in an oxidizing atmosphere.