JPH0216183B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a break ring for horizontal continuous casting, and more particularly to a break ring for horizontal continuous casting characterized in that a thermal expansion absorbing layer is provided on the outer periphery. <Conventional technology> In steel casting, the horizontal continuous casting method (hereinafter referred to as "horizontal continuous casting"), in which slabs are drawn horizontally from the bottom of the tundish, has lower equipment costs than the conventional vertical continuous casting method. It is gradually being put into practical use for this reason. As shown in FIG. 1, the break ring for horizontal continuous casting is used under very severe conditions, with the inner surface of the ring 4 being in contact with the molten steel 5 and the outer surface being in contact with the water-cooled mold 3. Various materials have been proposed for the break ring. <Problems to be Solved by the Invention> As a result of prototype break rings made of these various materials and tested, the present inventors found that all break rings made of alumina, zirconia, and silicon nitride failed to meet the shaded area 6 in Fig. 2. There were drawbacks such as cracking and peeling of the break ring, causing the peeled pieces to adhere to the surface of the slab, cracks occurring on the surface of the slab, and leakage of molten steel from cracks and peeled parts of the break ring. On the other hand, the above phenomenon was not observed with break rings made of boron nitride, but boron nitride has poor wear resistance, short life, and is difficult to sinter, so it must be sintered at high temperatures. Therefore, the manufacturing cost is high, and there are problems as a material for break rings as consumable items. The present inventors have investigated materials for break rings that are resistant to corrosion in molten steel and can replace boron nitride.
A prototype break ring made of a magnesia-carbon-silicon nitride composite with strength, elastic modulus, and thermal conductivity almost the same as boron nitride was used, but cracking and peeling still occurred. This was found to be due to the fact that the coefficient of thermal expansion of the prototype was approximately four times that of the boron nitride product. The break ring 4 for horizontal continuous casting is crimped and fixed to the mold 3. During use, the break ring is heated by the molten steel 5 and expands, but the outer periphery of the break ring is fixed to the mold 3.
Moreover, since the mold 3 is water-cooled and has a small amount of expansion, stress is generated on the contact surface of the break ring 4 with the mold 3 due to thermal expansion.
In particular, the shaded area 6 in FIG. 2 is heated by the molten steel 5 from two sides, and therefore generates larger stress. This stress exceeds the breaking strength of the break ring, so
Break rings are thought to cause cracking and peeling. The coefficient of thermal expansion of boron nitride break rings is very small, and they tend to shrink from room temperature to around 500℃, so the generation of thermal stress is small, causing cracks, cracks, etc.
No peeling occurs. Based on the above knowledge, in order to prevent damage to break rings made of ceramic materials with a large coefficient of thermal expansion, break ring 4 and mold 3 should be
We came to the conclusion that the problem could be solved by providing a layer (hereinafter referred to as an absorbing layer) that absorbs the thermal expansion of the break ring on the contact surface with the break ring. The conditions that this absorbent layer must meet are: (1) to shrink due to the compressive force caused by the expansion of the break ring;
(2) Since the break ring is press-fitted into the mold, it is slippery and does not damage the mold surface. Furthermore, it absorbs the distortion of the break ring due to crimping. (3) It is molten steel corrosion resistant. (4) Casting (5) It has oxidation resistance because it comes into contact with high-temperature gas during preheating of the tundish before starting, and (5) it has the ability to bond with the break ring. <Means for Solving the Problems> The present inventors have completed this invention as a result of various studies on the material, manufacturing method, thickness, etc. of the absorbent layer that satisfies the above conditions. The thermal expansion absorbing layer of this invention is a paste of boron nitride powder and an inorganic adhesive, boron nitride powder 50 to 97% by weight.
and one or two selected from the group of alumina, zirconia, magnesia, spinel, and silicon nitride.
The outer periphery of the break ring is made by kneading a mixed powder with 50 to 3% by weight of a refractory material of 50 to 3% by weight or above with an inorganic adhesive, or by adding inorganic fibers such as carbon fiber or alumina fiber to this kneaded material. It can be obtained by coating or by pasting inorganic fibers such as carbon fibers or alumina fibers on the break ring body using the above-mentioned kneaded material that does not contain carbon fibers or alumina fibers. As the carbon fibers or alumina fibers to be attached to the break ring, it is more preferable to use cloth woven with fibers. Boron nitride has excellent lubricity, oxidation resistance, and corrosion resistance for molten steel, and by using an inorganic adhesive, the absorption layer structure does not deteriorate due to oxidation even when heated to 200°C or more in an oxidizing atmosphere, making carbon fiber When used, it is also advantageous in terms of preventing oxidation of carbon fibers caused by preheated exhaust gas from the tundish. The type of inorganic adhesive used and the mixing ratio with boron nitride are appropriately selected and adjusted depending on the workability and the type and amount of the refractory powder used. After applying the above paste to a break ring or pasting a cloth with the paste, it is dried and heat treated in a non-oxidizing atmosphere to thermally stabilize the absorbent layer. This heat treatment is useful for preventing dimensional changes (especially shrinkage of the absorbent layer) caused by heating by the preheated exhaust gas of the tundish or by heating by molten steel after the break ring with the absorbent layer is crimped and fixed in the mold. This heat treatment temperature may be adjusted as appropriate depending on the type of inorganic adhesive used. The heat-treated break ring with an absorption layer is processed into a predetermined size and used. Note that the thickness of the absorbing layer may be appropriately set depending on the material and shape of the break ring. The break ring provided with the thermal expansion absorbing layer of the present invention can eliminate all stress and strain generated by thermal expansion due to heating of molten steel during use by the absorbing layer. Therefore, the main body of the break ring can be selected with a focus on materials that are resistant to molten steel corrosion, resulting in a significant improvement in durability compared to conventional break rings without an absorption layer or break rings made of boron nitride. . <Examples> The present invention will be explained in more detail with reference to Examples below. Examples 1 to 5 Break ring bodies made of materials shown in Tables 1 to 5 (the break ring bodies of Examples 3 to 5 were manufactured by compounding metallic silicon and reacting and sintering it in a nitrogen atmosphere) A paste prepared by adding 40 parts by weight of liquid sodium silicate to 100 parts by weight of boron nitride powder with a particle size of 10 μm or less was applied to the outer periphery to a thickness of 2 mm, and after drying, heat treatment was performed at 500° C. for 3 hours in a nitrogen atmosphere. The heat-treated break ring was machined to predetermined dimensions. The thickness of the absorption layer is Break Ring No.1 and No.
No. 2 was set to 1.0 mm, and Nos. 3 to 5 were set to 0.4 mm. The chemical composition of the absorption layer itself is BN50% by weight, SiO ₂ 37% by weight,
It contained 12% by weight of Na ₂ O, had a compressive strength of 133 Kg/cm ² , and had an adhesive strength of 63 Kg/cm ² to the break ring body.

[Table] Example 6 A break ring body corresponding to Example 5 was prepared by adding commercially available carbon cloth (plain weave, 0.41 mm thickness, graphitized) to 100 parts by weight of boron nitride powder and 60 parts by weight of sodium silicate. After pasting with paste and drying,
It was packed in carbon breeze and heat treated at 500℃ for 3 hours to form the desired dimensions. The thickness of the absorbent layer was 0.6 mm. Example 7 A paste obtained by adding an inorganic adhesive to boron nitride and a refractory material with a particle size of 10μ or less shown in Table 2 was applied to the break ring body, and Examples 1 to 5 were prepared.
A thermal expansion absorbing layer was formed on the break ring body using the same process as above. A 5 ton billet was cast using the obtained break ring, and the break ring body after the treatment was observed, and the results shown in Table 2 were obtained.

【table】

[Table] Example 8 A paste obtained by adding an inorganic adhesive to boron nitride with a particle size of 10μ or less and a refractory material with the composition shown in Table 3 was used to make the break ring body the same carbon as used in Example 6. A cloth was attached and heat treatment etc. were performed under the same conditions as in Example 6 to form a thermal expansion absorbing layer. A 5 ton billet was cast using this break ring, and the break ring itself was observed after the process, and the results shown in Table 3 were obtained.

[Table] Example 9 A paste was obtained by adding an inorganic adhesive and carbon fiber or alumina fiber to boron nitride with a particle size of 10μ or less and a refractory material in the formulation shown in Table 4, and this paste was applied to the break ring body. and Example 1~
A thermal expansion absorbing layer was formed on the break ring by performing the same treatment as in No. 5. A 5 ton billet was cast using the obtained break ring, and the break ring after the treatment was observed, and the results shown in Table 4 were obtained.

[Table] Comparative Examples 1 to 5 Break rings made of the materials shown in Table 1 and 1 to 5 without an absorbent layer were processed into predetermined dimensions. The break rings obtained in Examples 1 to 9 and Comparative Examples 1 to 5 were set, and a billet casting test of 90 mm diameter was conducted using steel type S45C. The break rings were all crimped and fixed to the mold with a pressure of 5 kg/cm ² . For all of the break rings of Comparative Examples 1 to 5, which do not have a thermal expansion absorption layer, adhesion of break ring fragments to the billet surface and cracks, roughness, etc. on the billet surface began to be observed about 2 to 3 minutes after the start of casting, and after about 5 minutes. It became impossible to pull it out. The condition of the break ring after the test was that corner chips on the contact surface with the mold were observed all over the circumferential direction, and internal cracks had also occurred. On the other hand, in all of the break rings of Examples 1 to 9 having a thermal expansion absorbing layer, a billet of 5 tons could be cast without any problem. After casting, the break ring had no corner chips or internal cracks that were seen in the comparative example, and the absorption layer had a step between the contact surface with the mold and other areas, and the absorption layer was affected by the expansion of the break ring body. The excellence of this invention was recognized.

[Brief explanation of drawings]

FIG. 1 is a sectional view between a tundish and a mold for horizontal continuous casting, and FIG. 2 is a diagram showing details of the contact portion between the break ring and the mold. 1... Tandate nozzle, 2... Intermediate ring, 3... Mold, 4... Break ring, 5
... Molten steel, 6 ... Corner chipping part of the break ring.

Claims (1)

[Scope of Claims] 1. A break ring for horizontal continuous casting, characterized in that a thermal expansion absorbing layer made of a kneaded material of boron nitride powder and an inorganic adhesive is provided on the outer periphery of the break ring. 2. A break ring for horizontal continuous casting according to claim 1, wherein the thermal expansion absorbing layer is made of a mixture of a kneaded material of boron nitride powder and an inorganic adhesive, and carbon fiber or inorganic fiber. . 3 Boron nitride powder 50~97 on the outer periphery of the break ring
% by weight and a mixed powder of 50 to 3% by weight of one or more refractory materials selected from the group of alumina, zirconia, magnesia, spinel, and silicon nitride, and an inorganic adhesive. A break ring for horizontal continuous casting characterized by having an expansion absorption layer. 4. The thermal expansion absorbing layer is made of a mixture of a mixed powder of 50 to 97% by weight of boron nitride powder, 50 to 3% by weight of a refractory material, an inorganic adhesive, and a mixture of carbon fiber or inorganic fiber. A break ring for horizontal continuous casting according to claim 3.