JP5081090B2 - Carbonless long nozzle - Google Patents

Description

  The present invention relates to a long nozzle used for pouring molten steel from a ladle into a tundish, and more particularly, to a carbonless long nozzle having a carbonless refractory disposed on the surface of an inner hole.

  Long nozzles are used under harsh conditions such as large thermal shock when pouring molten steel, so alumina-graphite refractories with excellent spalling resistance are used, and usually alumina is mainly used. Carbon bond refractories containing 15 to 40% by mass of graphite are used.

  On the other hand, in a steel type having a low carbon content such as extremely low carbon steel, the elution of carbon from the long nozzle into the molten steel deteriorates the quality of the steel as a product. For this reason, a long nozzle in which carbon is not contained on the inner hole surface of the long nozzle or a carbonless refractory having a carbon content of 10% by mass or less is disposed is used. Carbonless refractories generally include refractories composed solely of oxide materials mainly composed of alumina and containing silica, magnesia, etc., or these refractory materials contain a small amount of carbonaceous materials such as graphite and pitch. Refractories are used.

  However, the carbonless refractory does not contain graphite or contains 10% by mass or less, so that the coefficient of thermal expansion is larger than that of the long-nozzle main body refractory because the carbon content is low. For this reason, the phenomenon which gives a big thermal stress to a main body refractory by the thermal expansion of a carbonless refractory at the time of preheating before use or use starts, and the main refractory breaks down occurs.

  On the other hand, for example, in Patent Document 1, a cylindrical carbonless refractory is divided in the length direction, and joints are provided between the carbonless refractory and the nozzle body, and between the divided portions of the carbonless refractory. This joint prevents pre-heating before use and expansion absorption due to heating during use, thereby preventing the body material from cracking.

  Patent Document 2 discloses a nozzle for continuous casting in which an inner tube material having cracks and / or slits is arranged, and suppresses the generation of thermal stress by creating a room for releasing expansion in the circumferential direction of the inner tube material. , Preventing the body from cracking.

  Patent Document 3 discloses a long nozzle in which a carbonless refractory is disposed over the entire surface of the main body refractory that is a skeleton and is in contact with the molten steel on the surface of the inner hole. By making the apparent porosity 18% or more and forming a structure that reduces the strength at a temperature of 600 ° C. or higher, the thermal expansion when passing through the molten steel is alleviated and the spalling resistance is ensured.

Patent Document 4 discloses a straight immersion nozzle in which the inner diameter of the tip of the immersion nozzle is enlarged. It is described that the quality of the slab is improved and the nozzle clogging is effectively prevented.
JP-A-8-57601 JP 2000-301321 A JP 2006-130555 A JP-A-9-108793

  However, in the method of Patent Document 1, although the frequency of occurrence is low, cracks themselves may occur. Furthermore, there is a problem that the inner hole body is separated into a plurality of parts, and it takes time and labor to arrange them one by one on the main body via the mortar.

  In the nozzles of Patent Documents 2 and 3, since the inner hole body itself can absorb thermal expansion in the first use, the occurrence of cracks and cracks can be considerably improved, but the frequency of occurrence of cracks near the lower end of the long nozzle is low. There is a problem that cracks occur. It has also been found that the frequency of occurrence of such cracks and cracks increases at the time of reuse such as once cooling and reusing.

  Accordingly, the present invention provides a carbonless long nozzle that can reduce the occurrence of cracks and cracks at the lower end of the carbonless long nozzle in a carbonless long nozzle in which a carbonless refractory is disposed on the inner hole surface. With the goal.

  When the present inventors investigated the state after use about a carbonless long nozzle, it turned out that the crack and crack which the lower end part of the long nozzle made the origin have generate | occur | produced. Then, when the thermal stress analysis at the time of use was performed about this carbonless long nozzle by the finite element method, it turned out that the largest thermal stress has generate | occur | produced in the lower end part and the inner surface side. Regarding this cause, stress due to thermal expansion is concentrated on the lower end due to structural factors of the long nozzle having an opening at the lower end, and the carbonless refractory has a carbonaceous raw material content higher than that of the main body refractory. Since it is small, the thermal expansion coefficient and the elastic modulus are increased, and as a result, it is considered that a larger stress is generated on the inner surface side than the outer surface of the main body. Moreover, carbonless refractories have less effect of suppressing oversintering and slag infiltration due to carbonaceous raw materials, so the sintering reaction proceeds during use and the elastic modulus increases, so the generated stress tends to be higher. . Therefore, when considering the mechanism of crack generation, the lower end surface of the carbonless refractory on the inner surface side is positioned above the lower end surface of the main body, or the thickness of the lower end portion of the carbonless refractory is determined. It was confirmed that there was an effect of suppressing cracks and cracks with the lower end surface as a base point by reducing the size.

  That is, in one aspect of the present invention, a carbonless long material in which a carbonless refractory having a carbonaceous raw material of 10% by mass or less (including 0) is disposed on the inner surface of a main body refractory having a carbonaceous raw material of 15 to 40% by mass. In the nozzle, the carbonless refractory is a carbonless long nozzle in which a lower end surface of the carbonless refractory is located in a range of 20 mm to 100 mm from a lower end surface of the long nozzle body.

  When the lower end surface of the carbonless refractory is less than 20 mm from the lower end surface of the long nozzle main body, the stress suppressing effect of the lower end portion of the main body refractory is insufficient and the effect of suppressing cracks and cracks is insufficient, exceeding 100 mm. The effect of suppressing the occurrence of cracks and cracks is almost the same, but rather the adverse effect of the carbon pickup due to the main body refractory being exposed to the inner hole becomes a problem.

  The carbonaceous raw material of the main body refractory needs 15 to 40% by mass in order to obtain sufficient durability as a long nozzle. If the carbonaceous raw material is less than 15%, the spalling resistance is insufficient, and if it exceeds 40% by mass Strength and corrosion resistance are insufficient.

  In order to prevent carbon pickup, the carbonless refractory does not need to be used as much as the carbonaceous raw material is small. However, as the carbonless refractory is small, the spalling resistance is lowered. If it exceeds 10% by mass, which can be used at a mass% or less, the effect of suppressing the carbon pickup becomes worse. Further, the amount of the carbonaceous raw material used is more preferably 5% by mass or less from the viewpoint of enhancing the carbon pickup prevention effect.

  In carbonless long nozzles, cracks and cracks at the lower end that occur during use can be suppressed, so the frequency of interrupting casting operations is significantly reduced compared to conventional carbonless long nozzles, resulting in a more stable operation. it can.

  FIG. 1 is a longitudinal sectional view of a carbonless long nozzle according to the present invention. The carbonless long nozzle of the present invention is composed of a substantially cylindrical main body refractory 3 having a flange portion 31 at an upper portion, and a cylindrical carbonless refractory 4 disposed on the inner surface 1 of the main body refractory. In this carbonless long nozzle, the flange portion 31 is connected to a lower nozzle attached to a sliding nozzle device of a ladle, and the lower portion is used by being immersed in a tundish.

  The lower end surface 41 of the carbonless refractory is positioned above the lower end surface 32 of the main body refractory, and the distance is 20 mm or more and 100 mm or less. The carbonless refractory 4 is ideally disposed on the entire surface of the inner surface side of the main body refractory 3 in contact with the molten steel for the purpose of preventing carbon pickup, but near the joint surface with the lower nozzle of the flange portion 31. Does not have to arrange the carbonless refractory 4. Moreover, it is more preferable to arrange the carbonless refractory 4 at 80% (area ratio) or more of the inner surface 1 of the main body refractory. In addition, the inner surface 1 said here does not include the joint surface 6 with the lower nozzle of the flange part 31. Further, in FIG. 1, the main body refractory can be disposed between the lower end surface 41 of the carbonless refractory 4 and the lower end surface 32 of the main body refractory 3 to eliminate the step of the inner hole.

  Moreover, the main body refractory 3 can use the general alumina carbon refractory which mainly contains an alumina type raw material, and contains 15-40 mass% of carbonaceous raw materials. Specifically, it can be produced by using a refractory raw material mixture comprising 40 to 80% by mass of alumina-based material and 15 to 40% by mass of carbonaceous material. Moreover, 40 mass% or less of silica can be contained as a refractory raw material mixture in addition to the alumina-based raw material and the carbonaceous raw material, or one or more of magnesia, zircon and zirconia can be contained in an amount of 10 mass% or less. In addition to these, there is no problem if a metal generally used for a long nozzle or a boride such as boron carbide is used. The alumina-based material is at least one of alumina, mullite, zirconia mullite, and alumina zirconia. The carbonaceous raw material is graphite or amorphous carbon, and specifically, one of scale graphite, expanded graphite, synthetic graphite, soil graphite, pitch, tar, carbon black, carbon fiber, coke and the like. That's it. The main body refractory referred to in the present invention is a refractory constituting the main part constituting the skeleton of the long nozzle, and the refractory having a different material from the main body refractory when used in a part such as a slag line or a flange portion is except.

  The carbonless refractory 4 may contain a refractory containing no carbonaceous raw material or containing 10% by mass or less, more preferably 5% by mass or less. There is no particular limitation, and those used for refractories disposed on the inner hole surface of an immersion nozzle or a long nozzle can be used. For example, other than the carbonaceous raw material, one or more of alumina, mullite, zirconia mullite, alumina zirconia, magnesia, dolomite, zirconia, zircon, calcium zirconate, and calcium silicate can be used. In addition to these, there is no problem if a metal generally used for a long nozzle or a boride such as boron carbide is used. More preferably, it is 60 to 95% by mass of alumina-based material, 1 to 40% by mass of one or more of magnesia and alumina magnesia spinel, and 10% by mass or less (including 0) of carbonaceous material, more preferably 5%. % Or less (including 0) can be used. As a result, a carbonless refractory having a low coefficient of thermal expansion and excellent corrosion resistance is obtained, and the durability is improved.

  The carbonless long nozzle of this invention can be manufactured by a conventional method by using the above refractory raw material composition.

  For example, an organic binder such as phenol resin or furan resin is added to each of the above refractory raw material blends and kneaded to obtain respective kneaded products. These kneaded materials are divided into molds, and are integrally molded by CIP (Cold Isostatic Pressing) or the like, followed by firing in a non-oxidizing atmosphere at 1100 ° C. Moreover, after shape | molding a main body refractory material and a carbonless refractory material separately, it can also join through mortar etc.

  In addition, you may apply the method of this invention in the well-known carbonless long nozzle of patent documents 1-3. Suppresses cracking and cracking of the lower end of the carbonless long nozzle body even when the carbonless refractory sinters and becomes dense during use, increasing the coefficient of thermal expansion and increasing the elastic modulus. And durability is improved.

  In addition, when a material having a high coefficient of thermal expansion such as dolomite is disposed as the carbonless refractory, a known structure in which a thermal expansion absorption margin is secured between the main body refractory and the refractory can be employed.

  Table 1 shows the test results in the actual furnace of the carbonless long nozzle of the present invention. The long nozzle used in the test is the same as the carbonless long nozzle shown in FIG. And a refractory raw material composition comprising 39% by mass of alumina magnesia spinel, and 5 parts by mass of an organic binder (residual carbon ratio 35%) diluted with a phenol resin in a solvent is added to each refractory raw material composition and kneaded separately. The kneaded product is divided into an inner side and an outer side, put into the same mold, molded with CIP, dried, fired in a non-oxidizing atmosphere at 1100 ° C. after molding. The total length of the carbonless long nozzle is 1500 mm, the thickness of the main body refractory is 60 mm, the thickness of the carbonless refractory is 20 mm, and the inner hole at the lower end is 150 mm in diameter.

  Examples 1 to 4 and Comparative Examples 1 and 2 were manufactured by changing the position of the lower end surface of the carbonless refractory by changing a part of the mold used at the time of molding.

  In the actual furnace test, these long nozzles were attached to an actual ladle and preheated to about 600 ° C. before passing the molten steel. In casting, the long nozzle was allowed to stand at room temperature for 1 hour or more for each cast (for 4 cups of 350 t ladle), and then preheated to about 600 ° C. and used again. The bottom end of the long nozzle was observed for each cast and observed for cracks and cracks. Ten long nozzles were used for each.

  Moreover, the test piece was cut out from the carbonless long nozzle manufactured as described above, and the thermal expansion coefficient and elastic modulus were measured. The thermal expansion coefficient of the main body refractory at 1000 ° C. is 0.41%, the elastic modulus is 4.4 GPa, and the thermal expansion coefficient of the carbonless refractory at 1000 ° C. after being altered using 3cast is 0. The elastic modulus is .86% and 5 GPa. In the thermal stress calculation, for the carbonless long nozzles of Comparative Example 1 and Examples 1 to 3, the long nozzle was preheated to 600 ° C., and then the outflow of the molten steel was started. The thermal stress generated in the main refractory was analyzed using the finite element method under the condition that the temperature reached ℃.

  As shown in Table 1, in Comparative Example 1 in which the lower end surfaces of the carbonless refractory and the main body refractory were matched, the lower end crack occurred in 1 out of 10 in 3cast and in 3 out of 10 in 4cast. . Further, in Comparative Example 2 in which the lower end of the carbonless refractory was placed 10 mm above the lower end of the main body refractory, one lower end crack occurred in 4 casts. On the other hand, in Examples 1 to 4 in which the lower end surface of the carbonless refractory was installed 20 mm or more above the lower end surface of the main body refractory, no lower end crack was confirmed. Therefore, it was found that the lower end crack of the long nozzle can be suppressed by positioning the lower end surface of the carbonless refractory 20 mm or more above the lower end surface of the main body refractory, preferably 40 mm or more.

  In Example 4 in which the lower end surface of the carbonless refractory was installed 100 mm above the lower end surface of the main body refractory, the elution of carbon in the molten steel can be considered slightly. Carbonless long nozzles equipped with a carbonless refractory with a small amount of carbon are often used for the purpose of preventing carbon pickup. Therefore, in the present invention, the lower end surface of the carbonless refractory is not provided above 100 mm from the lower end surface of the main body refractory.

  FIG. 2 is a diagram showing the distribution of thermal stress by thermal stress analysis using the right cross section when the long nozzle is cut in the vertical direction, and one scale is 20 mm in both vertical and horizontal directions. The magnitude of the generated stress is color-coded as shown in the figure. For example, the stress in the darkest part is 6.9 MPa or more, and the next darkest part is 5.4 MPa or more and less than 6.9 MPa. From the left side, one scale is a carbonless refractory, and the rest is a main body refractory.

  In Fig.2 (a), it is a calculation result of the comparative example 1 with which the lower end surface of a carbonless refractory and a main body refractory correspond, and it turns out that the largest stress has generate | occur | produced inside the main body refractory lower end part. . The generated stress decreases as the lower end surface of the carbonless refractory moves upward, and it can be seen that the region with the highest stress is almost eliminated 40 mm above (FIG. 2C). In addition, in the calculation result of Example 1 in which the lower end surface of the carbonless refractory is located 20 mm above the lower end surface of the main body refractory, as shown in Table 1, the stress generated at the lower end is reduced to 4.3 MPa at the maximum. Furthermore, it can be seen from the stress distribution diagram of FIG. 2B that the stress at the lower end is greatly reduced. Further, the calculation result of Example 2 positioned 40 mm above is 3.5 MPa at the maximum, and in Example 3 positioned 60 mm above, the maximum is 3.3 MPa. Thus, it was found that the stress generated in the main body refractory is greatly reduced by positioning the lower end surface of the carbonless refractory 20 mm or more above the lower end surface of the main body refractory.

Table 2, performed on carbonless long nozzle refractory raw material formulation in Table 1 be different than, prepared in the same method as in Table 1, ten test under the same test conditions as in Table 1 The results are shown. The shape of the carbonless long nozzle from Example 5 to Example 8 is the same as that of Example 2, and is a type in which the lower end surface of the carbonless refractory is positioned 40 mm above the lower end surface of the main body refractory. Comparative Examples 3 to 6 use refractory raw material compositions corresponding to Examples 5 to 8, respectively, and have a shape in which the lower end surface of the carbonless refractory coincides with the lower end surface of the main body refractory.

  In Example 5, as a result of using 10 pieces in an actual furnace, there were no cracks or cracks at the lower end, and good results were obtained. On the other hand, the same refractory raw material composition as in Example 5 is used, but Comparative Example 3 in which the lower end surfaces of the carbonless refractory and the main body refractory coincide with each other is used in 4cast. Cracks occurred at the lower end.

  Similarly, the carbonless long slurs of Examples 6 to 8 did not crack at the lower end of the main body even when 4cast was used. On the other hand, two cracks occurred in the lower end portion in Comparative Example 4 while one was used in Comparative Example 5, and three in Comparative Example 6 were all used in 4cast.

It is explanatory drawing by the longitudinal cross-sectional view regarding the carbonless long nozzle of Examples 1-4. The thermal stress calculation result of a carbonless long nozzle is shown, (a) shows the comparative example 1, (b) shows Example 1, (c) shows Example 2, (d) shows the thermal stress calculation result of Example 3. .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner surface of main body refractory 2 Opening part 3 Main body refractory 31 Flange part 32 Lower end surface of main body refractory 4 Carbonless refractory 41 Lower end surface of carbonless refractory

Claims (1)

  In a carbonless long nozzle in which a carbonless refractory whose carbonaceous raw material is 10% by mass or less (including 0) is arranged on the inner surface of the main body refractory whose carbonaceous raw material is 15 to 40% by mass, A carbonless long nozzle whose lower end surface is located in the range of 20 mm or more and 100 mm or less upward from the lower end surface of the main body refractory.