JPH0641389B2 - Refractory for continuous casting of stainless steel - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a refractory used for a mold injection port or the like for connecting a mold for continuous casting of stainless steel and a tundish.

[Prior Art] Generally, in a continuous casting facility, for example, a horizontal continuous casting facility, as shown in the figure, a field nozzle 2 and a mold 3 provided on the lower side of a tundish 1 are made of a refractory material 4.
Molten steel 5 in the tundish 1 which is connected via
Passes through the field nozzle 2 and the refractory 4 and the mold 3
And is cooled in the mold 3 to form a solidified shell 6, which is then withdrawn and continuously cast.

The refractory 4 used in this continuous casting facility is required to have performance such as high thermal shock resistance, resistance to wettability with molten steel, and high corrosion resistance.

Conventionally, as the refractory for continuous casting, silicon nitride (S
i ₃ N ₄ ) containing aluminum nitride (AlN) and boron nitride (BN) as AlN—BN—Si ₃ N ₄ system sintered body (published in Japanese Examined Patent Publication No. 58-30265) and Si ₃ N ₄ AlN, BN and aluminum oxide _(Al 2 _{O 3)} made of _{AlN-BN-Al 2 O 3} -Si 3 N 4 based sintered body which contains the (JP 59-50074 discloses Shosai) is known Has been.

[Problems to be Solved by the Invention] However, the former AlN-BN-Si ₃ N ₄ system sintered body is melt-damaged during long-time casting of carbon steel or casting of stainless steel, and the latter. AlN-B
_{N-Al 2} O 3 made of _-Si 3 _{N 4} sintered body,
There is a problem that the stainless steel is melted and lost during long-time casting.

Such _{cause, AlN-BN-Si 3 N} 4 sintered body and _{AlN-BN-Al 2 O 3} -Si 3 N 4 based sintered to both inevitably of 0.5% by weight or more in the presence of body Iron (F
e), 0.1% by weight or more of titanium (Ti) and other unavoidable impurities.

That is, Ti of the unavoidable impurities is highly reactive with chromium (Cr) in the stainless steel and easily forms a low melting point substance, and Fe is easily absorbed in the high Cr steel.
Therefore, molten metal (molten steel) easily penetrates into the refractory,
The refractory is melted.

Therefore, the present invention, by limiting the upper limit of the amount of unavoidable impurities, especially the amount of specific impurities in the impurities, the amount of melting loss is drastically reduced, so that the corrosion resistance can be dramatically improved. It is intended to provide refractory materials for continuous casting of steel.

[Means for Solving the Problems] In order to solve the above problems, the present invention is a refractory for connecting a mold for continuous casting and a tundish, which is 2 to 50% by weight of aluminum oxide and aluminum nitride. 1-3
0% by weight, 3 to 30% by weight boron nitride, 0.5% by weight or less unavoidable impurities, and the balance being silicon nitride. Among these impurities, iron is less than 0.3% by weight and titanium is less than 0.1% by weight. And all of the raw material components consist of a sintered body obtained by sintering a raw material having an average particle size of 5 μm or less.

[Action]

In the refractory for continuous casting of the stainless steel of the present invention,
Titanium in the unavoidable impurities is highly reactive with chromium and forms a low melting point substance, and iron is absorbed into high chromium steel, and is less likely to be melted and damaged. The bondability is enhanced and the density is improved.

If Al ₂ O ₃ is less than 2% by weight, the corrosion resistance is not effective,
If it exceeds 50% by weight, the thermal shock resistance decreases. AlN
Like Al ₂ O ₃ , if less than 1% by weight, the effect of corrosion resistance is not exerted, and if more than 30% by weight, thermal shock resistance decreases.

BN contributes to thermal shock resistance, and if it is less than 3% by weight, its effect is not exerted, and if it exceeds 30% by weight, the strength of the sintered body is remarkably reduced.

When the unavoidable impurities exceed 0.5% by weight, the corrosion resistance is remarkably reduced, and particularly when Fe in the unavoidable impurities is 0.3% by weight or more and Ti is 0.1% by weight or more, the corrosion resistance is deteriorated due to melting loss. Remarkable.

Si ₃ N ₄ forms a sialon-based solid solution together with Al ₂ O ₃ and AlN, and improves the corrosion resistance to molten steel.

Further, when the average particle diameter of each of the above components exceeds 5 μm, the sintered body decreases and the pore diameter increases.

In order to manufacture a refractory for continuous casting, the above-mentioned components, that is, Al ₂ O ₃ , AlN, BN, and Si _{3 are used.}
N ₄ was mixed in a required ratio, sufficiently kneaded, and molded by an appropriate molding means, and then the molded body was heated to 1500 to 1800 ° C. in a non-oxidizing atmosphere (for example, argon or nitrogen gas).
Sintering at the temperature of about 1 to 10 hours. Also S
Instead of using i ₃ N ₄ , Si may be blended and manufactured by nitriding reaction sintering at a temperature of 1300 to 1500 ° C. in a nitrogen gas atmosphere.

[Effects of the Invention] As described above, according to the present invention, titanium in the unavoidable impurities has a higher reactivity with chromium to form a low melting point substance, and iron is absorbed in high chromium steel, as compared with the prior art. It is extremely unlikely to be melted and damaged, and the sinterability of the sintered body itself is improved and the densification is achieved, so that the corrosion resistance can be dramatically improved. High C
r Steel can be continuously cast for a long time.

[Examples] Samples of refractory for continuous casting of stainless steel according to the present invention (specimens Nos. 1 and 2) and conventional specimens of refractory for comparison (specimens Nos. 1 to 3) were compared. The basic compounding ratio shown in Table 1 was used, and the content of unavoidable impurities was controlled to manufacture.

Each sample was manufactured as follows.

First, each component having an average particle size of 5 μm or less shown in Table 1 was controlled in content of unavoidable impurities, and 500 gr was added to each sample at the basic mixing ratio shown in the same table, and each mixture was stirred and stirred. After thoroughly mixing using a crusher, an organic binder (for example, PVA) was added to these mixtures and uniformly kneaded to obtain a kneaded clay.

Then, each kneaded material is shaped into a prism of 20 mm (length) × 20 mm (width) × 120 mm (length) and 220 mm (outer diameter) × 190 mm (inner diameter) with a molding pressure of 1 ton / cm ² by a hydraulic molding machine. After being molded into a circular disk shape of × 15 mm (thickness) and dried, each of these molded bodies was subjected to a nitrogen gas atmosphere 17
The sample according to the present invention and the sample for comparison were manufactured by sintering at a temperature of 00 ° C. for 5 hours.

(1) Of the above specimens, the prismatic ones were used for measuring the corrosion resistance to molten steel.

Corrosion resistance test for molten steel is conducted by carbon steel (S50C) and austenitic stainless steel (SUS310: 25C).
r-20Ni) was melted in a high-frequency furnace at 10 kg each, and 1
Immerse the specimen in molten steel held at a temperature of 500 ° C and
After holding for a period of time, the erosion amount (melting loss amount) of the test piece was measured.

(2) In the case of a circular plate shape, it is set between the mold and the tundish in a horizontal continuous casting facility, the mold diameter is 212 mm, the drawing speed is 0.8 m / min, and the drawing length is 75 m.
Austenitic stainless steel (SUS30
About 20 tons of the round billet of 4) was cast, and the erosion amount by the solidified shell of the refractory material, that is, the disk-shaped specimen, at this time was measured.

The measurement results of the amount of erosion of (1) and (2) are shown in the table.

Therefore, the corrosion resistance to molten steel is
0.8 ~ 1.0 mm for carbon steel, 1.5 ~ for stainless steel
Whereas the refractory material according to the present invention is melted by 2.0 mm,
Carbon steel does not melt at all, and stainless steel has an extremely small melt loss of 0.1 mm or less, which shows that the corrosion resistance of the refractory material according to the present invention is dramatically improved.

Further, the corrosion resistance during continuous casting of stainless steel is 2.0 to 3.0 mm for the conventional refractory material, whereas the refractory material according to the present invention is extremely small, less than 0.1 mm. It can be seen that the corrosion resistance of the material is dramatically improved.

In addition, although the case where the shape of the refractory material for continuous casting is a circular disk shape has been described in the above embodiment, the refractory material is not limited to this, and the refractory material may have a square shape or another shape.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a horizontal continuous casting facility showing an example in which the refractory material according to the present invention is used. 1 ... Tundish, 2 ... Field nozzle 3 ... Mold, 4 ... Refractory 5 ... Molten steel, 6 ... Solidification shell

Front page continued (72) Inventor Isao Imai No. 1 Minamitou, Ogakie-cho, Kariya city, Aichi Toshiba Ceramics Co., Ltd. Kariya factory Company Steel Pipe Mill (72) Inventor Takeyoshi Sakane 1 Nishino-cho, Higashimukaijima, Amagasaki City, Hyogo Prefecture Sumitomo Kinzoku Kogyo Co., Ltd. Steel Pipe Mill (56) Reference JP-A-60-51669 (JP, A)

Claims (1)

[Claims] 1. A refractory for connecting a continuous casting mold and a tundish, which comprises 2 to 50% by weight of aluminum oxide, 1 to 30% by weight of aluminum nitride, and 3 to 3 of boron nitride.
30% by weight, 0.5% by weight or less of unavoidable impurities, and the balance being silicon nitride, iron is less than 0.3% by weight, titanium is less than 0.1% by weight, and all raw material components are average. A refractory for continuous casting of stainless steel, comprising a sintered body obtained by sintering a raw material having a particle size of 5 μm or less.