JPH0437452A - Nozzle for casting wide and thin slab - Google Patents

Abstract

PURPOSE:To provide a nozzle having excellent durability by incorporating refractory raw material having chemical composition of the specific wt% of Al2O3, ZrO2 and SiO2, the specific % of mesophase carbon and graphite having the specific particle diameter, kneading and forming, and burning under non- oxidizing atmosphere after drying. CONSTITUTION:The blending material containing 20-80 wt% the refractory raw material composed of mullite, baddelegite and corundum as essential mineral composition and the chemical composition of 25-85 wt% Al2O3, 10-70 wt% ZrO2 and 5-25 wt% SiO2, 3-15% the mesophase carbon having <= 50mum particle diameter and 5-40% the graphite and <= 50mum particle diameter over the whole blending material is kneaded and formed by using bonding material. Then, after drying, this is burnt under non-oxidizing atmosphere to manufacture the nozzle for casting a wide and thin slab. By this method, the nozzle having high thermal strength and excellent spalling resistance can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a casting nozzle with high hot strength used for casting wide thin-walled slabs.

[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 hot strength and excellent spalling properties.

Means 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 AI2. Si
Other methods have been developed, such as adding metals such as metals to develop metal-based bonds during the firing process of refractories, and increasing the molding pressure of refractories to make the structure denser.

[Problems to be Solved by the Invention] However, when the strength is improved by such a method, there is a problem that the elastic modulus of the material increases to the same extent as the strength improvement, or even more. An increase in elastic modulus means a decrease in spalling resistance. In a nozzle for casting wide thin-walled slabs, high strength and resistance to thermal shock are important, and sacrificing spalling resistance in order to increase strength is undesirable in actual use.

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 excellent spalling properties.

[Means for Solving the Problems 1] The present invention for solving the problems described above is characterized in that the main mineral phase consists of mullite, baddellite, and corundum, and Agaos
25-85% by weight, ZrO, 10-70% by weight, 3
10 □ Refractory raw materials with a chemical composition of 5 to 25% by weight (
(hereinafter abbreviated as ZRM); 9. Mesophase carbon with a particle diameter of 50 μm or less, 3-15% by weight; 1. Graphite, 5-40%;
This is a nozzle for casting wide thin-walled slabs characterized by kneading and molding a compound with a diameter of less than μm using a binder, drying, and then firing in a non-oxidizing atmosphere.

[Function] The main mineral phase of the present invention consists of mullite, baddellite, and corundum, and contains 25 to 85% by weight of Al2Js, Z
r0. Contains 20-80% by weight of ZRM having a chemical composition of I C1-70% by weight, Sin, and 5-25% by weight. As shown in Japanese Patent Publication No. 59-19067, this raw material has a coefficient of thermal expansion of 7 x 10~'/'C from room temperature to 1000°C, and a coefficient of thermal expansion of 2 to 4 x 10-'/'C from 1000 to 1600°C. '/°C, has low thermal expansion especially at high temperatures, and has excellent durable poling properties.

When the content of ZrO□ is less than 10% by weight, the amount of zirconia precipitated inside or around the mullite or corundum crystal is small, resulting in poor corrosion resistance, and when the content exceeds 70% by weight, ZrO□
Because O□ exists in a monoclinic system, there is abnormal expansion,
Durable polling performance is poor.

The content of this ZRM in the blended raw materials is 20 to 80% by weight.
stipulated in If it is less than 20% by weight, a sufficient effect cannot be obtained, and if it exceeds 80% by weight, the content of carbon raw materials such as graphite will decrease, resulting in insufficient durable poling properties as a nozzle.

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 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 micromembrane phase is effective in improving strength, and at the same time, it is possible to prevent a decrease in durable poling property by suppressing an increase in elastic modulus.

Mesophase carbon exhibits a strong bonding effect due to the coalescence of mesophase spheres and the void filling effect due to softening and melting when heated during firing of refractories, forming strong carbon bonds.

This carbon bond is a soft carbon bond derived from pitch, which causes little increase in elastic modulus and is effective in improving durable poling property. The Menphase carbon used is
It is necessary to use materials that have not yet coalesced into bulk mesophase by heating. For this reason, the heat treatment temperature is 3
It is necessary that the temperature is 00 to 500°C, and the sphere size was set to 50 μm or less in order to define the stage before the coalescence of memphas progresses and the sphere size increases.

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 is insufficiently produced and the memphis content is low, volatile matter due to pitch will increase, forming pores when firing the refractory and weakening the structure. Content is over 50%, volatile content is 3
It needs to be 0% or less.

Memphase carbon, which is effective in improving strength and suppressing increases in elastic modulus, cannot achieve sufficient effects when used in amounts less than 3% by weight, and if used in excess, carbon's inherent low abrasion resistance may be reduced. , there are problems such as dissolution into molten steel,
If the amount exceeds 15% by weight, the strength decreases, so the amount used is limited to 3 to 15% by weight, and the particle diameter is set to 50 μm or less.

Graphite includes natural scaly graphite and beaded graphite.

Artificial graphite obtained by heat treating coke or the like can be used, but scaly graphite is preferable from the viewpoint of corrosion resistance and spalling resistance. If the graphite content is less than 5% by weight, the durable lag properties of graphite will not be exhibited, and if it is more than 40% by weight, high strength will not be obtained and the resistance to molten steel will deteriorate.

Next, by setting the particle diameter of all the formulations to 50 μm or less, sufficient strength cannot be obtained if the particle diameter of 0 particles, which have very high strength, exceeds 50 μm.

The maximum particle diameter is even smaller than 50 μm, e.g. 3
Although it is technically possible to set it to 0 um or 10 tLm, manufacturing such graphite and refractory raw materials is economically inferior and not practical.

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

The blended refractory raw materials shown in Table 1 were cross-wired using a phenol resin as a binder, molded, and then reduced and fired to obtain a wide thin slab casting nozzle.

In Example 1.2, no cracks were generated in the durability poling test, and the hot bending strength also showed a high value.

Comparative Examples 1 and 2 have a maximum particle size larger than the claimed range,
Although the spalling resistance is good, the hot bending strength shows a relatively low value, and in Comparative Examples 3 and 4, the content of menphase carbon is outside the claimed range, and cracks were not observed in the spalling resistance test. In addition, the hot bending strength is low, both of which are inferior to those of the examples.

Example 3.4 is within the scope of the present invention and has high strength (and good spalling resistance), but Comparative Example 5.6, in which the ZRM content is lower than or exceeds the scope of the present invention, has high strength (and good spalling resistance). Polling performance decreases.

[Effects of the Invention] As explained above, the casting nozzle according to the present invention has higher thermal strength and better spalling properties than conventional nozzles, and is exposed to high-temperature molten steel and furthermore As a nozzle for casting wide, thin-walled slabs that are subject to mechanical or thermal shocks such as internal and external pressure, it is highly durable and exhibits excellent performance.

Claims (1)

[Claims] The main mineral phase consists of mullite, baddellite, and corundum, Al_2O_325-85% by weight, ZrO_2
20-80% by weight of a refractory raw material having a chemical composition of 10-70% by weight, SiO_25-25% by weight, and a particle size of 5%.
Contains 3 to 15% by weight of mesophase carbon and 5 to 40% of graphite, each having a particle diameter of 50 μm or less.
1. A nozzle for casting wide thin-walled slabs, characterized in that a compound having a particle size of .mu.m or less is kneaded and formed using a binder, dried, and then fired in a non-oxidizing atmosphere.