JPS5921575A - Refractories for continuous casting - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refractory that connects a tundish and a mold in continuous casting equipment, a so-called joint ring, which has excellent corrosion resistance especially in continuous casting of stainless steel. This article relates to continuous casting refractories that exhibit excellent performance.

Conventionally, silicon nitride or boron nitride refractories have been widely used as refractories that connect the tundish and mold in horizontal continuous casting equipment, but recently silicon nitride refractories have been developed to improve their thermal shock resistance. This has become strongly desired, and products made by mixing boron nitride and sintering it have come to be provided. Such a sintered body exhibits sufficient thermal shock resistance when casting general carbon steel, but if stainless steel, especially high Cr steel, is to be cast, it may be necessary to use silicon nitride. There was a problem in that the melting loss progressed significantly, making it extremely difficult to carry out long-term operation. On the other hand, there is some research into improving this by using boron nitride as the main material, but since it is originally manufactured using a hot press method, there is a problem with casting costs, and the fact is that it has low wear resistance. There are several flaws, and we have yet to fully overcome them. Therefore, the current situation is that thermal shock resistance has been improved to some extent by using silicon nitride and boron nitride in combination, but in continuous casting of stainless steel, especially high Cr steel, it is difficult to melt refractories. Damage is unavoidable, leading to deterioration of surface quality due to damage to the refractory, and sometimes localized melting damage to the refractory, causing breakout, making it impossible to contribute to stable operation.

The present invention has been made in view of this situation, and aims to provide a refractory that can strongly resist corrosion damage, particularly corrosion damage caused by the Cr component in molten steel. It is something.

The refractory of the present invention that has achieved properties suitable for the above purpose is a stabilized zirconia sintered material that may contain up to 20% by weight (hereinafter simply referred to as "related") of boron nitride. The gist lies in the fact that the body is the subject.

The present inventors have conducted various studies on the reasons why silicon nitride sintered bodies are relatively easily eroded and damaged by molten stainless steel.
Under high heat conditions exceeding 500℃, silicon nitride undergoes chemical transformation due to the reaction between Cr in stainless steel and silicon nitride, turning into a low point substance and being eroded away. I found something useful. Therefore, as long as silicon nitride was placed in the booth, it was thought that it would be difficult to completely prevent the chemical formation caused by Cr, so we started thinking about sintering as an alternative to this and using a completely different idea. Thinking that this may be necessary, we fabricated prototype sintered refractories of various compositions and tested their corrosion resistance in molten stainless steel. As a result, it was found that the sintered body obtained by uniformly dispersing Al2O3, MgO, ZrO2, etc. in silicon nitride exhibits extremely good corrosion resistance against molten stainless steel. was found to be extremely promising. However, ZrO2 itself has the disadvantage of transformation expansion, and there are many problems when viewed as a raw material for manufacturing joint rings, which are used in areas that require high precision, such as between the tundish and the mold. Do you get it. Therefore, Al2O3 and MgO
It has superior corrosion resistance (particularly corrosion resistance against molten stainless steel) and excellent high-temperature strength and toughness, and has a high heat insulation effect due to its low thermal conductivity. Although it was expected that the surface quality of slabs would be improved by suppressing the formation of solidified shells inside refractories, it is not necessarily easy to apply the present invention to the target field. There was that aspect.

Therefore, we searched for something that would not cause the above-mentioned transformation expansion, and arrived at stabilized zirconia refractory material.

Stabilized zirconia refractory material itself is well known and is generally manufactured by adding CaO or MgO, which have poor thermal shock resistance, to ZrO2, but from an industrial perspective, there have been various manufacturing methods. has been proposed, and for example, a cast material is used by sintering a material obtained by a slurry casting method, an extrusion method, or a cold press method, etc., regardless of whether it is dense or porous. Available. Also, using fused and stabilized zirconia, after crushing and adjusting the particle size, preferably blending them into a densely packed structure, adding a small amount of organic binder, mixing and shaping, drying and baking. The present invention can also be applied to the present invention.

If stabilized zirconia is used for this purpose, a refractory with excellent thermal shock resistance and erosion resistance can be obtained, but if boron nitride, which has high thermal conductivity and low coefficient of thermal expansion, is added, thermal shock resistance and spalling resistance are further improved. These effects of boron nitride can also be achieved by adding a small amount of boron nitride, so setting a lower limit is not particularly meaningful from a technical point of view, but 5 to 10
%, the above effects become noticeable. On the other hand, as for the upper limit, if it exceeds 20%, the strength as a refractory will decrease, so it should be kept below 20%.

Since the present invention is configured as described above, even in continuous casting of stainless steel, especially steel containing 10% or more of Cr, the present invention has good thermal shock resistance and melting resistance as a refractory. It has excellent properties such as durability and spalling resistance, making it possible to safely complete continuous casting without causing accidents such as breakouts.

Next, examples of the present invention will be shown.

165φ x 150φ x 20t (mm) made of stabilized zirconia containing 10% boron nitride and 70% CaO
The ring-shaped sintered body was placed in the tundish nozzle and the curve of the mold. 1 stainless steel SUS304) 4.5 tons
When it was poured at 570° C. and continuously cast at a drawing speed of 1.3 m/min, approximately 80 m was able to be completely cast. During this period, no cracks were observed in the sintered body, and no melting damage occurred, so the surface quality of the slab was extremely good. For comparison, similar continuous casting was performed using a ring made of silicon nitride sintered body and a ring made of boron nitride sintered body, and in the case of the former, breakout occurred at 10 m.
In the latter case, the operation was forced to stop due to increased pulling resistance at 20 m. When we investigated the reason for the increase in pulling resistance, we found that
Boron nitride refractories are locally worn away by solidified grains,
Molten steel was inserted between the refractory (joint ring) and the mold.

Applicant: Kobe Steel, Ltd. Agent Patent Attorney Hisaichi Ueki

Claims (2)

[Claims] (1) A refractory for continuous casting, which is a refractory for connecting a tundish and a mold of horizontal continuous casting equipment, and is mainly composed of a stabilized zirconia sintered body. (2) A refractory that connects the tundish and mold of horizontal continuous casting equipment, characterized by being mainly composed of a stabilized zirconia sintered body containing 20% by weight or less of boron nitride. Refractories for continuous casting.