JP2520190B2 - Refractory manufacturing method for continuous casting equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a refractory material for continuous casting equipment, which is used as a member such as a mold weir or a nozzle of continuous casting equipment.

Conventional technology Since members such as mold weirs and nozzles in continuous casting equipment are used under severe conditions, conventional materials are mainly silicon nitride (Si ₃ N ₄ ), boron nitride (BN), or a mixture of both. Has been used. The properties of these materials are shown in Table 1.

However, among the above materials, Si ₃ N ₄ has insufficient thermal shock resistance, and BN and a mixture of Si ₃ N ₄ and BN have disadvantages such as poor wear resistance. _It cannot be said that ₃ N ₄ is sufficient, and it can be said that all of them have low hardness.

Therefore, the inventors of the present invention have proposed, in Japanese Patent Laid-Open No. 2-111664, a refractory material for continuous casting equipment which satisfies the heat resistance, thermal shock resistance, wear resistance and the like required as a material for continuous casting equipment.

Problems to be Solved by the Invention Normally, conditions that can be used for nozzles for continuous casting equipment, at least bending strength is 5kgf / mm ² or more,
Thermal shock resistance of 650 ° C or higher, Vickers strength of 6
It is necessary to satisfy the four conditions of being 00 or more and withstanding multiple castings.

However, even a refractory material satisfying the above components may have a large amount of molten steel adhered thereto or may have low wear resistance.

It is an object of the present invention to solve the above problems and provide a method for producing a refractory product for continuous casting equipment, which can reliably produce a refractory material suitable for continuous casting equipment.

Means for Solving the Problems In order to solve the above-mentioned problems, the method for producing a refractory material of the present invention comprises 5 to 20% by weight of boron nitride powder and 2 to 20% by weight of zirconium, hafnium, titanium and chromium. At least one powder selected from borides, 5 to 20% by weight of a sintering aid powder, and the rest of silicon nitride powder are kneaded and dried, and then molded into a predetermined shape. The gas is contained in an amount of 5 to 30% by volume and is fired in a nitrogen gas atmosphere at atmospheric pressure or higher.

Action Among the above refractory components, BN that imparts thermal shock resistance is 5
If the amount is less than 10% by weight, the effect is insufficient, and if the amount exceeds 20% by weight, the strength tends to decrease, and it is necessary to blend in the range of 5-20% by weight. Further, the borides of Ti, Zr, Hf and Cr, which impart hardness and improve the melting resistance, do not have a satisfactory effect at less than 2% by weight, and the thermal shock resistance deteriorates at more than 20% by weight. Is also inappropriate. Furthermore, as sintering aids for Si ₃ N ₄ , MgO, Al ₂ O ₃ , SiO ₂ , MgAl ₂ O
_At least one kind of oxides such as ₄ , Y ₂ O ₃ and ZrO ₂ may be selected and used, and the blending ratio is required to be 5 to 20% by weight. If it is less than 5% by weight, the sintering becomes insufficient and the strength becomes low, and if it exceeds 20% by weight, the thermal shock resistance deteriorates due to the increase of the coefficient of thermal expansion, and in either case, it is not suitable.

Then, the atmosphere gas for sintering these is changed to N ₂ gas.
The reason why the Ar gas is contained in an amount of 5 to 30% by volume is that if the Ar gas is less than 5% by volume, the added boride becomes a nitride in the heating process and the molten metal resistance is significantly lowered.
This is because if it exceeds the volume%, Si ₃ N _{4 of the} base material may decompose and sublime to generate bubbles, and if the atmosphere is lower than atmospheric pressure, Si ₃ N ₄ may decompose and sublime.

Example Si ₃ N ₄ powder (average particle size 0.8 μm), Al ₂ O ₃ powder (average particle size 0.5 μm), MgO powder (average particle size 0.5 μm), BN powder (average particle size 1 μm), ZrB ₂ , CrB ₂ , TiB ₂ and HfB ₂ powders (each having an average particle size of 1 μm) were compounded to the composition shown in Table 2 below, and then ball milled for 16 hours in ethanol. The resulting slurry was dried at 120 ° C for 10 hours, then uniaxially molded in a mold with a diameter of 100 mm at a pressure of 300 kgf / cm ² , and further CIP molded at a pressure of 3 ton / m ² (cold static pressure compression molding). . Formed compacts at a specific amount at 1800 ° C and 1.5 atm
Sintering was performed for 2 hours in an N ₂ gas atmosphere containing Ar gas. The bending strength at room temperature, thermal shock resistance, and Vickers hardness of the obtained sintered body were measured, and the results are shown in Table 2.

In Table 2, the thermal shock resistance (JIS R 1601 bending test pieces (3 x 4 x 38 mm) 4 pieces in different temperature electric furnace
After bending and holding for 15 minutes, the test piece was placed in water at 0 ° C., and a bending test was performed on each of the test pieces.

In the first test, a sintered body that was fired according to the components and conditions shown in Table 2 was used, with an outer diameter of 150 mm, an inner diameter of 100 mm, and a height of 150-2.
It is a cylindrical body of 00 mm and has many slits (width 100 μm) on the bottom.
By molding a nozzle in which the nozzle was formed and pouring 50 kg of molten stainless steel continuously 5 times with this nozzle, and visually observing this nozzle after use, the continuous use durability of the refractory was evaluated.

Among the comparatively shown samples in Table 2, No1 is the one with a small addition amount of boride in the component, No4 is BN in the component
No. 5, No. 5 shows a large amount of BN in the components, No. 2 shows that the firing atmosphere is only N ₂ , and No. 3 shows that the firing atmosphere contains a large amount of Ar.

As is clear from Table 2, it was found that the sample Nos. 1 to 5 of the comparative examples used as the nozzles in the first experiment were not suitable for use.

Moreover, it was found from the results of the first experiment that samples No6 to No15 produced by the materials and methods described in the claims were extremely suitable for continuous casting equipment. It should be noted that in Sample Nos. 2 and 3, even though the material composition was a sintered body that satisfied the scope of the claims, the composition was greatly affected by the composition of the firing atmosphere and was not suitable for continuous casting equipment. The experimental results show the effect of the atmosphere on the sintered body.

Separately from this first experiment, 25 × 50 × 10
Cut it to ^t mm, slide it into the end face of the twin roll mold, and fit it into the sliding contact part of the short side weir that constitutes the molten steel receiver, 350 k
A second experiment was carried out in which molten stainless steel of g was continuously cast 5 times at a casting speed of 30 m / min. As a result of visually observing the sintered body after the second implementation, almost the same result as the first experiment was obtained, but only the sample No. 15 had a large amount of wear. Therefore, the wear amount of the sliding contact surface increases as the amount of BN increases close to 30% by weight, as in this sample No15, and the portion of the continuous casting equipment where there is no direct sliding contact other than molten steel such as the molten steel. It was found that it can be used, but is not suitable for direct sliding contact.

Effects of the Invention As described above, according to the present invention, BN powder that imparts thermal shock resistance, and Z that imparts hardness and improves melting resistance
R, Hf, Ti, Cr boride powders, sintering aids, and Si ₃ N ₄ powders can be kneaded and dried in an appropriate amount and then molded to prevent the formation of nitrides in the heating process. Since it was fired in a nitrogen gas atmosphere containing Ar gas in a range capable of preventing decomposition of Si ₃ N ₄ and above atmospheric pressure, the bending strength, thermal shock resistance, hardness and resistance required for continuous casting equipment were With excellent balance of abrasion resistance and corrosion resistance, it is possible to reliably manufacture refractory materials that can be stably used for a long time for continuous casting equipment.

Claims (1)

(57) [Claims] 1. Boron nitride powder in an amount of 5 to 20% by weight, at least one powder selected from borides of zirconium, hafnium, titanium and chromium in an amount of 2 to 20% by weight, and 5 to 20% by weight in sintering. Auxiliary powder and the remaining silicon nitride powder are kneaded and dried, and then molded into a predetermined shape, and this molded product is baked in a nitrogen gas atmosphere containing 5 to 30% by volume of argon gas and at atmospheric pressure or higher. A method for producing a refractory material for continuous casting equipment, comprising: