JPS61205671A - 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 [Field of Industrial Application] The present invention relates to a refractory used in a mold inlet, etc. that connects a mold and a tundish in continuous casting equipment.

[Prior Art] Generally, in continuous casting equipment, for example, horizontal continuous casting equipment, as shown in the figure, a field nozzle 2 and a mold 3 provided on the lower side of a tundish 1 are connected to a refractory material 4.
The molten steel 5 in the tundish 1
is injected into a mold 3 through a field nozzle 2 and a refractory 4, cooled in the mold 3 to form a solidified shell 6, and drawn out for continuous casting.

The refractory 4 used in this continuous casting equipment has properties such as high thermal shock resistance, difficulty in getting wet with molten steel, high corrosion resistance, and ease of processing as it satisfies the requirements for high dimensional accuracy. is required.

Conventionally, the above-mentioned refractory for continuous casting has been disclosed in Japanese Patent Application Laid-Open No. 46-7
Reactive sintered silicon nitride (3i s N4) sintered bodies and JP-A No. 15332/1983, etc.
A hot-pressed boron nitride (8N) sintered body described in Publication No. 0-27448 has been generally used, but the former 3i 3 N4 sintered body has poor heat resistance, and the latter The BN sintered body had a problem of low hardness and poor wear resistance.

In order to deal with the above problem, a St 3 N4-BN sintered body containing BN in Si 3 N4 was developed.
20575 Publication), Si 3 containing aluminum nitride (AIN) J5 and BN in Sr 3N4
N4-AIN-BN series sintered body (JP-A-56-12966
6), Si: +N+, AIN, alumina (A
12O2) and BN-based sintered body containing Si3N4-A-N-A1303-BN (Japanese Patent Application Laid-Open No. 59-5007
A refractory made of the following materials (published in Publication No. 4) is known.

[Problems to be Solved by the Invention] However, although the Si 3 N4-BN-based sintered body exhibits corrosion resistance when cast into carbon steel, it suffers from corrosion when cast into stainless steel. be. Moreover, the Si 3 N4-AuN-BN based sintered body has the problem of being damaged by melting during long-time casting of carbon steel or casting of stainless steel. Furthermore, Si s
The N4A-N-Al203-BN-based sintered body (Sialon-BN-based sintered body) has a problem of being melted and damaged during long-term casting of stainless steel.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a refractory for connecting a continuous casting mold and a tundish,
Aluminum nitride 1-80% by weight, boron nitride 1-50%
% by weight, 1 to 30% by weight of clay mineral, and the balance is silicon nitride.

[Function] A refractory made of a sintered body of Si 3 N4 alone exhibits corrosion resistance against carbon steel, but chemically reacts with stainless steel and is eroded. Therefore, by incorporating AILN, which has corrosion resistance against molten steel, into 3i 3 N4, the corrosion resistance is significantly improved. The higher the m content of A-N, the higher the corrosion resistance; however, if it exceeds 80% by weight, the strength decreases, and if it is less than 1% by weight, no corrosion resistance is exhibited.

However, the one made of Si3N4-AIN sintered body,
When stainless steel and other materials are cast for a long period of time, they are eroded and damaged, and their elastic modulus increases, causing spalling cracks due to thermal shock.

Therefore, by uniformly dispersing BN in the Si 3 N4-AIN sintered body, the elastic modulus is reduced and the thermal shock resistance is improved. The finer the BN particles, the better, and if the content exceeds 50% by weight, the strength will drop sharply.
And if it is less than 1 mm%, thermal shock resistance is not exhibited.

When a clay mineral such as a montmorilloid group such as bentonite or acid clay or an illite group such as sericite or muscovite is added to the Si3N4-AiN-BN-based sintered body, it becomes difficult to wet with molten steel, and the clay mineral Alumina (A1203 > and silica (Si 02
) reacts with Si 3 N 4 and AIN to form sialon and reduce the coefficient of thermal expansion. In addition, the alkaline component of clay minerals reacts with Si 3 N 4 to produce a glass phase, improving sinterability and blocking the pores during use to prevent molten steel from entering. - functions as a lubricant. Therefore, the corrosion resistance of the refractory is improved. When the content of clay mineral exceeds 30% by weight, the amount of glass phase produced increases and the high-temperature properties deteriorate, and when it is less than 1% by weight, it becomes easy to wet and the sinterability decreases.

In addition, in order to make a refractory for continuous casting, each of the above-mentioned constituent components, namely Si 3 N4 and AIN.

BN and clay minerals are blended in the required proportions, thoroughly kneaded, and molded using an appropriate molding means, and the molded body is heated to 1450 to 18
This is done by sintering at a sintering temperature in the range of 00°C for about 1 to 10 hours. Further, the manufacturing method is not limited to the sintering in the non-oxidizing atmosphere using 3i 3 N4, but may be produced by reaction sintering in nitrogen gas using 3i.

[Effects of the Invention] As described above, according to the present invention, the corrosion resistance and thermal shock resistance of continuous casting refractories can be significantly improved compared to the conventional technology, and damage to the refractories due to solidified shells can be prevented.
As a result, not only long-term casting of stainless steel but also continuous casting of high-alloy steel can be made possible.

[Example] Specimens of refractories for continuous casting according to the present invention (specimens 1 to 1)
5) and conventional refractory specimens (specimen NIL1) for comparison were manufactured with each composition shown in the upper row of Table 1.

Table 1 Each specimen was manufactured as follows.

First, each component shown in Table 1 was mixed with 500 or of each sample at the mixing ratio shown in the same table, and after thoroughly mixing each compound using a stirring and crushing machine, an organic binder ( PVA) was added and kneaded uniformly to form a clay.

Next, each clay was molded into 220 mm (outer diameter) x 190 Jl by a hydraulic forming machine at a forming pressure of 1 ton/c1i! (inner diameter)
X15g+(thickness) circular plate shape and 20M(@)X2
After forming into a prismatic shape of 0 shoes (width) x 120 shoes (length) and drying, place it in a nitrogen gas atmosphere for 1700 minutes.
□ A specimen according to the present invention and a specimen for comparison were manufactured by sintering at a temperature of 5 hours.

(1) As shown in the middle row of Table 1, the physical properties of the refractory according to the present invention show that the porosity is lower and the strength is much higher than that of the conventional refractory.

(2) Among the specimens, the prismatic ones were used for corrosion resistance tests against molten steel and for measuring the contact angle with molten steel.

The corrosion resistance test for molten steel was performed by melting 10 kg each of carbon steel (S50C) and stainless steel (SLIS321) in a high frequency furnace, immersing the specimen in the molten steel held at 1550°C, and holding it for 1 hour. The erosion depth was measured.

In addition, the contact angle with molten steel was measured by placing carbon steel and stainless steel on a specimen, raising the temperature to 1500°C and maintaining this temperature, and measuring the contact angle at that time using a high-temperature microscope.

As shown in the lower part of Table 1, the corrosion resistance test results for conventional refractories are 3.0rras for carbon steel and 5.0rras for stainless steel.
．． The corrosion depth is 0 mm, whereas the refractory according to the present invention is not corroded at all in carbon steel, and is 0 mm in stainless steel.
The corrosion depth is extremely small, 1 mg+ or less, and it can be seen that the corrosion resistance of the refractory according to the present invention has been dramatically improved.

(3) The circular plate-shaped specimen was set between the mold and tundish of horizontal continuous casting equipment, and
Austenitic stainless steel (SIJ
S321: 20 tons of round billets of 25Cr -2ON+ were cast.

Table 2 shows the degree of corrosion due to the strong shell of the refractory at this time.

Table 2 As is clear from Table 2 above, the depth of corrosion due to the solidified shell on the inner surface of the refractory reaches up to 5.0 taa in the case of conventional refractories, which is so large that it damages the end face of the mold and is stable. Whereas casting is impossible, the refractory according to the present invention has only a small amount of 0.1 to 0.2 degrees, and there is no problem with casting at all, the mold surface is also good, and stable casting is possible. I understand.

In addition, in the said Example, the case where the shape of the refractory was made into circular plate shape was demonstrated, but it is not limited to this and the refractory may have a rectangular or other shape.

[Brief explanation of drawings]

The figure is a schematic sectional view of a horizontal continuous casting facility showing an example in which the refractory according to the present invention is used.

Claims (2)

[Claims] (1) A refractory that connects the mold and tundish for continuous casting, consisting of 1 to 80% by weight of aluminum nitride, 1 to 50% by weight of boron nitride, 1 to 30% by weight of clay minerals, and the balance silicon nitride. A refractory for continuous casting characterized by the following. (2) The refractory for continuous casting according to claim 1, wherein the clay mineral is a montmorillonite group.