JPH0437448A - Nozzle for casting wide thin-walled slabs - Google Patents

Abstract

PURPOSE:To provide a nozzle having excellent durability by kneading and forming the specific wt% of mesophase carbon, single element or compound of Al and Si, boron carbide, graphite and the other refractoriness raw material and bonding material and burning after drying. CONSTITUTION:The blending material of 3-15 wt% mesophase carbon, 3-10 wt% single element or compound Al and Si, 0.2-2.0 wt% boron carbide, 5-40 wt% graphite and the other refractoriness material and the bonding material is kneaded and formed. After drying this, the burning is executed to manufacture the nozzle having excellent hot strength and modulus of elasticity 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.

[Conventional technology]

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 shock, so there is a risk of cracking due to these shocks. Therefore, the nozzle is required to be made of a material that has particularly high hot 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 Aj! , S
A method of adding metals such as i to develop metal-induced bonds in the firing process of refractories, and increasing the molding pressure of refractories (
However, methods have been developed to make the organization more precise.

[Problem to be solved by the invention]

However, if the strength is improved by this method,
There is a problem in that the elastic modulus of the material increases to the same degree as or even more than the increase in strength. 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 to solve the problem]

The present invention for solving the above problems includes mesophase carbon in an amount of 3 to 15% by weight, Aj? , 3 to 10% by weight of simple substance or compound of Si, and 0.2 to 2.0% by weight of boron carbide.
This is a wide thin slab casting nozzle characterized by kneading and molding 5 to 40% by weight of graphite and other refractory raw materials and a binder, drying and firing.

[For production]

First of all, mesophase carbon is petroleum-based.

Alternatively, when coal-based pitch is heated, free carbon and hydrocarbons aggregate in a certain alignment, producing liquid crystals with optical anisotropy. This is a sphere with a size of several μm to several 10 μm called a micromesophase. 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 micro-mesophase 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 mesophase 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. The mesophase carbon to be used must be one 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 the sphere size is set to 50 μm or less in order to define the stage before the coalescence of the memphas progresses and the sphere size increases. If the heat treatment is excessive, the mesophase spheres will coalesce, and the bonding effect will not be fully exerted when used in refractories (1°) On the other hand, if mesophase formation is insufficient and the mesophase content is low, it is due to the pitch. The mesophase content is 50% because the volatile content increases, forming pores and weakening the structure when inviting refractories.
It is necessary that the volatile content be at least 30% by weight.

The use of mesophase may be effective even in a small amount, but if used in excess, there are problems such as the low wear resistance of carbon and its dissolution into molten steel, so the appropriate amount to use is in the range of 3 to 15% by weight.

According to Japanese Patent Application No. 1-90241, it is possible to obtain a high-strength immersion nozzle by adding the above-mentioned mesophase carbon, but when considering a nozzle for casting wide and thin slabs, when performing high-speed casting, A large amount of molten steel flows through the inner hole of the thin slit nozzle, generating a large internal pressure. A nozzle that will not break even under this internal pressure is required, and high strength is also required.

The present inventors used Al and Si as a means of improving strength.

As a result of various studies on the amounts of B and C added, it was found that 3 to 10% by weight of AN or Si alone or as a compound, and 0.2 to 10% by weight of boron carbide.
It has been found that it is appropriate to add 2.0% by weight.

Al2. When Si metal is added to a carbon-containing refractory such as a nozzle for casting wide thin-walled slabs, it generates carbides and nitrides during the firing process of the refractory. Moreover, these products develop as connective tissue in the voids of the refractory, and therefore exhibit great strength. Further, bonding using carbides and nitrides is less likely to deteriorate even at high temperatures and is advantageous in imparting hot strength. If the amount used is less than 3% by weight, the effect will be small, and if it is in excess, the spalling resistance will decrease. The amount used is 3 to 10% by weight or appropriate.

Regarding B and C, part of them becomes oxides during the firing process of the refractory and forms a ceramic bond with the aggregate, and a part of them forms a carbon bond with the binder of the refractory. Especially when combined with metal as in the present invention,
Forms a strong bond between aggregate, metal and binder.

However, if it is in excess, a large amount of B2O3 is produced, which reacts with the plaster to form a low-melting substance, resulting in a decrease in hot strength. The appropriate amount used is 0.2 to 2.0% by weight.

As graphite, natural graphite scales, earthy graphite, artificial graphite obtained by heat treating coke, etc. can be used.
Scale graphite is desirable from the viewpoint of corrosion resistance and spalling resistance. If the graphite content is less than 5% by weight, the slag resistance 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.

〔Example〕

The present invention will be explained based on examples.

The blended refractory raw materials shown in Table 1 were kneaded with a phenol resin as a binder to prepare a molding compound.

A nozzle for casting wide thin-walled slabs was obtained through an isostatic press → drying → firing process.

Examples 1 to 4 contain 8% by weight of metals and 0.5% by weight of boron carbide.
The mesophase carbon content is 3 to 15% by weight. All of them show high hot strength, while the improvement in elastic modulus is suppressed, and in Examples 5 and 6, which have good spalling resistance, the amount of boron carbide is increased. While the hot strength gradually decreases, the elastic modulus increases.

In Comparative Example 1 in which the amount of boron carbide exceeds the claimed range, the elastic modulus is high and the hot strength is significantly reduced.

Similarly, Comparative Examples 2 to 6 have high elastic modulus (low hot strength) and are inferior to Examples.

〔Effect of the invention〕

As explained above, the casting nozzle according to the present invention has superior hot strength and elastic modulus compared to conventional nozzles, and can be exposed to high-temperature molten steel and even exposed to mechanical or thermal shocks such as internal and external pressure of molten steel. As a nozzle for casting wide, thin-walled slabs that are subjected to high temperatures, it is highly durable and can exhibit excellent performance.

Agent Patent Attorney Masaaki Akizawa 1 other person

Claims (1)

[Claims] 3-15% by weight of mesophase carbon, Al, Si
3 to 10% by weight of a single substance or compound of , and 0.0% of boron carbide.
A nozzle for casting a wide thin slab, characterized in that it is made by kneading and molding 2 to 2.0% by weight of graphite, 5 to 40% by weight of graphite, other refractory raw materials, and a binder, drying and firing.