JPS60127053A - Refractories for connection of horizontal continuous casting device - Google Patents

Abstract

PURPOSE:To provide hollow refractories for connection to be interposed between a tundish and a casting mold which withstand a long-time continuous operation and to suppress intrusion of impurity inclusions into a molten metal by using a refractory blank material contg. a specific amt. of carbon and a consisting of the balance oxide to form the specific part of said refractories. CONSTITUTION:An intermediate ring (cylindrical member 4b) formed of a refractory blank material contg. 5-40wt% carbon and consisting of the balance substantially oxide is disposed at the feed nozzle side in the part nearer than the break ring (cylindrical member 4C) adjacent to a casting mold 1 where a solidified shell having a relatively thin wall can be formed. The costly ceramic break ring is thus made shorter than in the prior art and the cost is reduced. The damage of the refractories adjacent to the break ring by the solidified shell is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refractory for connecting horizontal continuous casting equipment, and in particular to a horizontal continuous casting equipment that can withstand long-term continuous operation and suppress the incorporation of impurity inclusions into cast products. This relates to refractories for connections.

The horizontal continuous casting method is a method in which slabs are drawn in a nearly horizontal straight line, and compared to the currently mainstream vertical and curved continuous casting methods, the equipment height is lower, making it easier to operate. It is easy to maintain, and the equipment is relatively small and the construction cost is low. ■The mold is directly connected to the side of the tundish (however, in reality, it is connected via a connecting refractory), The static pressure inside the tundish is directly applied to the molten steel in the mold, which improves the accuracy of the slab shape.
Since secondary oxidation does not occur, the stagnation level of the cast slab is high, and other advantages have recently been reconsidered, and research is being actively carried out to put it into practical use.

However, although it has the above-mentioned features, it also has some unique drawbacks, and one of the biggest drawbacks is that "connection refractories connecting the tundish and the mold (hereinafter simply referred to as connection refractories)" ), the characteristics required are very strict.

In other words, the connecting refractory must (a) have a high degree of dimensional accuracy in order to fit between the tundish and the casting mold to ensure a secure connection between the two, and (b) be able to withstand sudden temperatures during injection of molten steel. (c) It has thermal shock resistance that can withstand changes.
In addition to being required to have corrosion resistance that can withstand continuous operation at high temperatures and for long periods of time, (d) the cooling effect of the mold also extends to the connecting refractory side, causing damage to the inner peripheral surface of the refractory. A solidified shell is also formed on the side, but in order to suppress the friction with the solidified shell and allow the slab to be pulled out smoothly, the inner surface must be smooth and dense, and at the same time, it must be smooth and dense enough to prevent molten steel from being inserted. It is also required that the material has low wettability. Expensive ceramics such as BN-based materials, Si, and N4-based materials are known as materials that meet these required characteristics, and if the fireproof connections and the entire object are made of such materials, there will be no operational problems. It almost never occurs. However, since the materials are extremely expensive, an excessive economic burden is imposed.

On the other hand, among the above required characteristics, (a) and (d) are required only near the contact area between the connecting refractory and the mold, so the connecting refractory is constructed by a pair of a feed nozzle and a break ring. The connection side with the mold has the above (a)
A break ring made of expensive ceramic material having the characteristics of ) to (a) is arranged, and an inexpensive refractory material (zircon) having the characteristics of (b) and (c) is arranged to connect the break ring and the kundish. It is customary to use a feed nozzle made by A. For example, FIG. 1 is a longitudinal cross-sectional view of the main parts showing an example of the arrangement of such conventional connection refractories, showing a kundish (not shown in the drawing) and a mold 1.
is concentrically connected to a feed nozzle 2 and a break ring 3, and the feed nozzle 2 is made of an inexpensive oxide refractory material, while the break ring 3 is made of an expensive ceramic refractory material. .

The inner diameters of the feed nozzle 2, the break ring 3, and the mold 1 are formed so as to increase successively along the flow direction of the molten steel, so as to suppress as much as possible the turbulence of the molten steel flow that occurs at the stepped portions. With such a connection structure, the feed nozzle 2 has the required characteristics of (b) and (C) above,
Furthermore, since the break ring 3 has the required characteristics (a) to (d) above, almost no problems occur during steady operation. However, in the early stages of casting when the temperature of the eye-drilling nozzle 2 has not risen sufficiently, or in the late stages of casting when the molten steel temperature drops, or even when the withdrawal stop time is delayed due to operational abnormalities, the solidified shell may not reach the feed nozzle 2. As the feed nozzle 2 grows, the feed nozzle 2 made of an oxide-based refractory having sufficient characteristics (a) and (d) is relatively easily damaged due to sticking and pulling out of the solidified shell. In particular, the stepped portion 2a at the end of the feed nozzle 2 on the drawing side is easily damaged. Once local damage occurs, a solidified shell is inserted into this area and the damage progresses rapidly.Furthermore, the joint boundary with the break ring 3 is damaged and the solidified shell is inserted, and finally the break ring 3 is damaged. This leads to serious accidents such as destruction and breakouts. Furthermore, the oxide refractories mixed into the molten steel due to the breakage of the feed nozzle 2 become impurity inclusions and significantly deteriorate the quality of the casting.

The easiest way to avoid these problems would be to make the break ring 3 sufficiently long, but this would (1) increase the amount of expensive ceramics used, leading to a rise in cost; (11) the break ring 3 Depending on the material, problems such as a decrease in thermal shock resistance may occur as the length increases. Therefore, there is a need to develop a technique that can solve the above-mentioned problems without causing such obstacles.

The present invention was completed as a result of various studies aimed at preventing damage to the feed nozzle under the above-mentioned circumstances. The refractory is constructed by combining two or more cylindrical members in series, and the inner diameter of each cylindrical member is larger as it is placed closer to the mold. The second cylindrical member counted from the mold side is either [I] formed of a fire-resistant material containing 5 to 40% by weight of carbon and the remainder substantially consisting of an oxide, or (■) A refractory material containing 5 to 40% by weight of carbon, 20% by weight or less of a high melting point carbide and/or a high melting point carbide, and the remainder being essentially an oxide. The main points are as follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and effects of the present invention will be described in detail below with reference to the drawings. FIG. 2 shows a typical embodiment of the present invention, in which the connecting refractories are cylindrical members 4a, 4b, 4
The cylindrical member 4a corresponds to the feed nozzle 2 in FIG. 1, and the cylindrical member 4c corresponds to the break ring 3 in the same figure. The structure is such that a cylindrical member 4b is interposed as an intermediate ring between these cylindrical members 4a and 4C. These cylindrical members 4a, 4b, and 4c are formed so that the closer they are disposed to the mold 1, the larger the inner diameter thereof.

The use of the intermediate ring 4b is an important requirement in order to minimize the step difference at each connection boundary, thereby reducing stagnation of the molten steel flow and suppressing the formation of solidified shells. Further, in the present invention, the cylindrical member 4c adjacent to the mold 1 has the above-mentioned required characteristics (
It is made of ceramics and is equipped with a) to (d).
The cylindrical member 4b next to it (#) (i.e., the second one counting from the mold 1 side) is made of the refractory material shown in CI) or 3 above, and the cylindrical member 4a is made of a normal oxide-based refractory material. . The reason for changing the materials of the cylindrical members 4 as 4 bs 4 c in this manner is as follows. That is, according to the knowledge obtained by the present inventors using the conventional connection example shown in FIG.
Since a solidified shell is likely to form on the mold 1 side, the required characteristic (a) is not met.
There are strong requirements for (d) and ceramics with these characteristics must be used, but the molten steel temperature on the feed nozzle 2 side is higher than that on the mold 1 side, and even if a solidified shell is formed, the wall is thin. Therefore, the degree of damage during the formation and extraction of the solidified shell is quite small. Therefore, first of all, the break ring 3 is divided into two parts and the required characteristics (
The idea is to form the mold 1 side, where a) and (d) are truly required, from ceramics, and the feed nozzle 2 side from ordinary oxide-based refractories. However, even on the feed nozzle 2 side, a considerable amount of solidified shell is not generated.

Therefore, although the above (b), (c) and (d) are important as the required characteristics of the ring 3 disposed in the feed nozzle 2, the required characteristic of (d) is on the mold 1 side. A higher level of performance is not required than those placed adjacent to the . In addition, it goes without saying that in consideration of economic efficiency, the material for the ring should be selected from inexpensive materials. Based on this knowledge, we searched for various relatively inexpensive materials that met the above-mentioned required characteristics, and as a result, we came up with the above-mentioned CI) or hammered fire-resistant material. However, the essential component of the fire-resistant material [I] is 5 to 40% by weight of carbon, and the refractory material of [I] contains 20% by weight of high-melting point carbide and/or carbon.
Or a high-melting point nitride is added, with the remainder being an oxide-based refractory.The reason for stipulating this requirement is explained in the following passage. In other words, carbon here refers to carbon that has been partially or completely graphitized by high-temperature treatment.
Oxide/carbon-based refractories made by combining these with oxides such as alumina, silica, magnesia, and zirconia are extremely inexpensive compared to ceramics, but have excellent wear resistance and
Thermal shock resistance and erosion resistance against molten slag are fairly good, and if it contains 5% by weight or more of carbon, it satisfies the characteristics required for the cylindrical member 4b disposed on the feed nozzle side. However, if the carbon content exceeds 40% by weight, the melting loss due to dissolution and diffusion of carbon into the molten steel becomes significant, and the purpose cannot be achieved. Also, high melting point carbides and nitrides (e.g. S 1c1B, C, Sis N,
, A.I.N.

Adding an appropriate amount of BN, etc.) further improves wear resistance and thermal shock resistance, but if it exceeds 20% by weight, sinterability deteriorates and spalling is more likely to occur, and it is also economically disadvantageous. . The type of oxide that is the remaining component does not matter as long as it is heat resistant, but typical examples include alumina, silica, magnesia, zirconia, etc. alone and mixtures thereof.

In this way, in the present invention, the break ring (cylindrical member 4c in Fig. 2) adjacent to the mold 1 is also chipped on the feed nozzle side, and a specific By arranging the intermediate ring (cylindrical member 4b) made of a fire-resistant material, the expensive ceramic break ring can be made shorter than before, reducing costs, and the intermediate ring (cylindrical member 4b) made of fire-resistant material Damage caused by the solidified shell of the refractory can be suppressed, allowing continuous casting to be performed stably for a long period of time, and the quality of slabs is improved by preventing inclusion of impurity inclusions caused by damage to the refractory. be able to. In the example shown in Fig. 2, the intermediate ring disposed between the feed nozzle and the break ring is made of the above-mentioned [■] or the tamped fire-resistant material.
CI) or City] fire-resistant materials are not so expensive compared to ordinary oxide-based fire-resistant materials, so a feed nozzle placed directly adjacent to the break ring 3 as shown in Figure 1 is suitable. It is also effective to form the entire part 2 from the above-mentioned CI'l or tamped fire-resistant material.

Next, an experimental example will be shown.

Experimental Examples In the connection structure shown in Figs. 1 and 2, various changes were made to the feed nozzle 2 (cylindrical member 4a) and break ring 3 (cylindrical member 4c), or these and the intermediate ring (cylindrical member 4b). We investigated the damage to the stepped portion caused by the solidified shell when horizontal continuous casting was performed under the following conditions.

[Continuous casting conditions]

Casting temperature: 1550℃ Slab diameter: 110mmφ Pulling speed: z, 3m/min Test molten steel: SUS 304.5 tons The results are summarized in Table 1.

In Table 1, Experiments 1 to 8 are examples in which the feed nozzle was directly connected to the plaque ring without using an intermediate ring, and the material of the feed nozzle was changed. For those molded with a normal oxide-based compound such as Anopena (experiment hh1.2 and grains, there was significant collapse and damage at the stepped portion of the feed nozzle.Also, even if the feed nozzle contains carbon, the When the amount of carbon is less than 5M (Experiment No. 3), thermal shock resistance and wear resistance are insufficient, while when the amount of carbon exceeds 40% by weight (Experiment No. 6), the carbon content in the molten steel is insufficient. Elution and diffusion become significant, and damage to the stepped portion progresses rapidly.In contrast, if the feed nozzle contains an appropriate amount of carbon (Experiments Na4 and 5), the damage to the stepped portion is extremely slight. can do.

Experiments 9 to 21 are examples in which an intermediate ring was interposed between a feed nozzle made of an oxide refractory material and a ceramic plaque ring, and the intermediate ring was formed of an ordinary oxide refractory material. In both cases (Experiment N [19 and 10)] and one made of composite refractories with a carbon content of less than 5% by weight (Experiment No. 11), there was significant damage at one part of the step between the intermediate ring and the plate ring. , where the intermediate ring is molded from a composite refractory that meets the specified requirements of the present invention (in experiments N [112 to 20, damage to the stepped portion can be suppressed to a low level. Especially on the inner surface of the intermediate ring, the thin wall However, a considerable amount of solidified shell is generated, but it is better to use a refractory containing a small amount of high melting point carbide (or high melting point nitride) with an appropriate amount of carbon (Experiment Nn113).
~21), damage to the stepped portion can be further suppressed.

[Brief explanation of drawings]

FIG. 1.2 is a schematic vertical cross-sectional view showing an example of the arrangement of connecting refractories. 1... Mold 2... Feed nozzle 3... Plaque ring 2a... Step portion 4a... Cylindrical member (feed nozzle) 4b... Cylindrical member (intermediate ring

Claims (2)

[Claims] (1) A connecting hollow refractory interposed between a tundish and a mold in a horizontal continuous casting device, the refractory being constructed by combining two or more cylindrical members in series, and each The inner diameter of the cylindrical member is made larger as it is disposed closer to the mold, and the second cylindrical member counted from the mold side contains 5 to 40% by weight of carbon, with the remainder being substantially composed of oxides. A refractory for connecting horizontal continuous casting equipment, characterized in that it is made of multi-layered refractory material. (2) A connecting hollow refractory interposed between a tundish and a mold in a horizontal continuous casting device, the refractory being constructed by combining two or more cylindrical members in series, and each The inner diameter of the cylindrical member is made larger as it is disposed closer to the mold, and the second cylindrical member counted from the mold side contains 5 to 40% by weight of carbon, 20% by weight or less of high melting point charcoal, and/or A refractory for connecting a horizontal continuous casting apparatus, characterized in that it is made of a refractory material containing a high melting point nitride and the remainder being substantially an oxide.