JP2010179340A - Method for removing non-metallic inclusion in steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for removing non-metallic inclusions present in molten steel in a tundish inexpensively without incurring any operational trouble. <P>SOLUTION: In the continuous casting of steel, as shown in the figure, a shape comprising an alumina-based refractory 13 is fixed to and installed on either or each of a bed 11 and a sidewall 12 in a tundish 2, and non-metallic inclusions contained in the molten steel are deposited on the alumina-based refractory 13 installed in the tundish and removed. In this condition, the alumina-based refractory 13 for depositing the non-metallic inclusions contains ≥60% alumina. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for removing non-metallic inclusions in steel by adsorbing them onto an alumina refractory which is alumina graphite placed in a tundish.

  Conventionally, various efforts have been made to increase the cleanliness of steel. Nonmetal inclusions are lifted by the application of RH degassing method during ladle refining, or by increasing the residence time of the molten steel in the tundish, and flow into the immersion nozzle. There are various methods, such as a method for preventing the above-mentioned problem and a method for removing the ceramic filter by installing it in the outflow path. If the capacity in the tundish is increased, it takes time for the molten steel injected into the tundish to flow into the immersion nozzle, so the possibility of non-metallic inclusions rising by the increase in the residence time can be increased. It is possible and widely adopted. However, since the longer residence time also promotes the temperature drop in the molten steel in the tundish, it leads to instability of quality and operability other than cleanliness. There is a limit to the means of increasing the residence time. Further, a method of removing a non-metallic inclusion by installing a ceramic filter in the outflow path is effective to some extent, but it cannot be said that it is sufficient in terms of durability and effect.

  In addition, for example, by blowing an inert gas in the molten steel passage in the tundish while electromagnetically stirring the molten steel, the bubbles of the blown inert gas are refined, and the refined gas bubbles are made minute. There has been proposed a method of floating minute nonmetallic inclusions by bringing them into contact with nonmetallic inclusions (see, for example, Patent Document 1). This method requires that the electromagnetic stirring coil to be used be mounted on all tundishes. However, in reality, a large number of tundishes are often used. Therefore, it is inevitable that mounting electromagnetic stirring coils on all tundishes will increase the cost considerably.

  In addition, there is a method in which a lower weir is provided in the tundish so as to promote the floating of minute nonmetallic inclusions. However, in this method, the molten steel in the region surrounded by the lower weir cannot be cast until the end, so it must be scrapped, and there is a problem that the casting yield is deteriorated. Thus, when actually considering from a viewpoint of manufacturing cost, these methods are not very methods that can be introduced in actual operation.

  Furthermore, based on the knowledge that nonmetallic inclusions are easily adsorbed on alumina refractories, a method has been proposed in which spherical alumina refractories are introduced into steel and nonmetallic inclusions are effectively removed ( For example, see Patent Document 2.) In this method, the specific gravity is set so that the spherical alumina-based refractory does not enter the immersion nozzle, that is, the immersion nozzle due to the molten steel flow in the tundish, so that it floats freely in the molten steel. . This is because if a spherical alumina-based refractory penetrates into the immersion nozzle, the supply of molten steel to the mold will be reduced and casting becomes impossible.

  By the way, although this patent document 2 is not touched, the point which becomes a problem by this method is a case where the specific gravity of the spherical alumina-based refractory is too small to be lifted. This is because one of the purposes of using tundish in the casting process is to remove non-metallic inclusions. However, during actual casting, a considerable amount of non-metallic inclusions are floating on the surface of the molten steel in the tundish. For this reason, when the ball | bowl which is a spherical alumina type refractory contacts this part, this ball | bowl of this alumina type refractory will adsorb those nonmetallic inclusions. After the adsorption, the ball further migrates in the molten steel, and there is a possibility that the non-metallic inclusions adsorbed on the surface layer of the ball during the migration become a larger lump and peel off. For this reason, when tundish powder is used as a heat insulating material in the tundish or when there is slag, the method of using this alumina refractory ball will adsorb these, so it is an unexpected method It is. In other words, the most important thing in the method of Patent Document 2 is to use an alumina refractory ball having a specific gravity that does not sink or float when the ball floats in the molten steel in the tundish. Yes, this is indispensable, but in reality it is extremely difficult and nearly impossible.

Japanese Patent Laid-Open No. 11-179497 Japanese Patent Laid-Open No. 09-206895

  The problem to be solved by the present invention is to provide a method for removing non-metallic inclusions present in molten steel in a tundish at low cost and without causing operational troubles.

  The means of the present invention for solving the above-mentioned problems is a method in which an alumina-based refractory such as alumina graphite is installed on a side wall or a floor in a tundish, and nonmetallic inclusions in steel are adhered to them.

  That is, in the invention of claim 1, in continuous casting of steel, a shape made of an alumina refractory is fixed and installed on one or both of the side wall and the floor in the tundish, and contained in the molten steel. This is a method of removing non-metallic inclusions by attaching them to an alumina refractory.

  According to a second aspect of the present invention, the alumina-based refractory to which non-metallic inclusions are adhered is an alumina-based refractory containing 60% or more of alumina. This is a method of removing inclusions.

  The reason and principle of the configuration of the present invention will be described. Adhesion of non-metallic inclusions to alumina-based refractories made of alumina graphite or the like is well known. Even if it is once covered with nonmetallic inclusions by adsorption, the adhesion of nonmetallic inclusions further proceeds due to the affinity of the nonmetallic inclusions themselves, and the present invention utilizes this fact. By fixing the alumina refractory to the side walls and floor of the steel, the alumina refractory does not float and drift on the molten steel surface, so the adhering nonmetallic inclusions peel off and reenter the molten steel. And there is no entry into the mold from the immersion nozzle.

  In the means of the present invention, a shaped object made of an alumina-based refractory that adsorbs and adheres non-metallic inclusions in molten steel is fixedly installed on one or both of the side wall and the floor in the tundish. Therefore, the nonmetallic inclusions contained in the molten steel in the tundish are adsorbed by these installed alumina refractories and removed from the molten steel. At this time, in particular, by using an alumina-based refractory containing 60% or more of alumina, the degree of adhesion of nonmetallic inclusions is further improved, and the nonmetallic inclusions are removed from the molten steel.

It is a figure which shows typically a continuous casting installation and a lump rolling installation. (A) is a perspective view which shows typically a part of tundish which installed the alumina-type refractory on the floor, and (b) is a perspective view which shows the other shape body of an alumina-type refractory. It is a perspective view which shows typically a part of tundish which installed the alumina-type refractory on the floor and the side wall. It is a graph which shows the adhesion degree with respect to the alumina content rate in an alumina-type refractory by comparing with an index. It is a figure which compares and shows the difference of the oxygen content index in steel with respect to use of the alumina refractory from which an alumina content rate differs.

  EMBODIMENT OF THE INVENTION The form for implementing this invention is demonstrated below with reference to attached drawing.

  The process shown as an embodiment of the present invention includes, for example, pouring refined molten steel shown in FIG. 1 into the tundish 2 from the ladle 1, and pouring the molten steel from the tundish 2 into the mold 4 with the immersion nozzle 3. After the continuous casting is cooled while being drawn out, it is cut into a slab 5 of an appropriate length by a cutting machine 6, cooled by a conveyor cooler 8 by a bloom cooler 8, and then heated by a heating furnace 9, and then a block rolling mill 10 is a method in a continuous casting process and a block rolling process in which the block is rolled in pieces. In this continuous casting process, 19 of an alumina-based refractory 13 having the shape shown in FIG. 2A is used on the floor 11 which is the bottom surface of the tundish 2 (all having the same alumina content at the occasion of casting). 3 or 31 pieces of alumina-based refractory 13 having the shape shown in FIG. 3, 19 pieces on the floor 11 and 12 pieces on the side wall 12 are placed on the mold 4 from the tundish outlet 14 by the immersion nozzle 3. About 4000 tons of standard S40C to S45C steel types were successively cast. In this case, Table 1 shows the casting conditions of Examples 1 to 4 and Comparative Example 1 below. The shape body of the alumina-based refractory 13 is a head cone in FIG. 2A or the embodiment in FIG. 3, but may be a cylindrical body shown in FIG.

  Examples 1 to 4 are shown in Table 1 using alumina-based refractory 12 having an alumina content of 50%, 60%, and 70% (remaining components are carbon and silica), respectively. Each was cast under casting conditions. Further, as Comparative Example 1, casting was performed under casting conditions in which the alumina refractory 13 was not used. After these castings, under the casting conditions of Examples 1 to 3, all oxides (alumina is 95% by mass or more) adhering to the surface of each alumina refractory 13 are recovered and recovered. The total weight of these oxides was measured and compared as an adhesion degree index to the surface of the alumina refractory 13. When the oxide was recovered by lightly tapping with a one-handed hammer, only the attached oxide could be easily separated from the surface of the alumina refractory 13 and recovered.

  In Examples 1 to 3, the total amount of oxides deposited on all 19 alumina-based refractories 13 is summarized. The adhesion degree index of the deposited alumina weight is plotted on the vertical axis, and the alumina content (%) is plotted on the vertical axis. A bar graph shown on the horizontal axis is shown in FIG. When the alumina content rate is 70%, the adhesion degree index is 9.7 for 60%, 3 for 50%, and the alumina content when the alumina content level reaches 50%. It can be seen that the effect of installing the refractory 13 on the floor 11 of the tundish 2 is greatly reduced. On the other hand, as in Comparative Example 1 of Table 1, the alumina refractory 13 was not installed on the floor 11 of the tundish 2 as in the conventional method, and the others were cast under the same conditions as in Examples 1 to 3.

  Next, in the case of Examples 1 to 3 using the respective alumina-based refractories 13 having an alumina content of 50%, 60%, and 70%, and an alumina content of 70% installed in the floor of Example 3 In addition to the alumina refractory 13 of the above, the average amount of oxygen in the steel in each of Example 4 in which 12 pieces of alumina refractory 13 having an alumina content of 70% were installed on the side wall, and the alumina refractory as in the conventional method The average amount of oxygen in the steel when the object 13 was not installed on the floor 11 of the tundish 2 was compared, and these are shown in FIG. In this case, the oxygen content index in the average steel when the alumina refractory 13 is not installed is 10.

  As shown in FIG. 5, the oxygen content index in steel in the case of Comparative Example 1 in which the alumina refractory 13 was not installed on the floor 11 of the tundish 2 was 10, and the alumina refractory containing 50% alumina. In the case of Example 1 in which 13 was installed on the floor 11 of the tundish 2, the steel oxygen content index was 9.8, and the steel oxygen index was almost the same. On the other hand, the oxygen content index in steel in the case of Example 2 in which the alumina refractory 13 containing 60% alumina was installed on the floor 11 of the tundish 2 was 8.1, and the 70% alumina-containing alumina refractory 13 The oxygen content index in steel in the case of Example 3 in which was installed on the floor 11 of the tundish 2 was 8.0. Furthermore, in addition to the 70% alumina-containing alumina refractory 13 being installed on the floor 11 of the tundish 2, the oxygen in the steel in the case of Example 4 in which the side wall 12 is also provided with the 70% alumina-containing alumina refractory 13 is provided. The quantity index was 7.2. In these cases, when the alumina-based refractory 13 was installed on the floor 11 of the tundish 2, the amount of oxygen contained in the molten steel decreased, and a clear improvement effect of the molten steel in the tundish 2 was observed. In addition, the oxide adhering to the periphery of the alumina-based refractory 13 does not float on the molten metal surface in the tundish 2, and the adhering oxide does not fall into the molten steel. High slabs could be cast.

DESCRIPTION OF SYMBOLS 1 Ladle 2 Tundish 3 Immersion nozzle 4 Mold 5 Cast slab 6 Cutting machine 7 Conveyor 8 Bloom cooler 9 Heating furnace 10 Bulk rolling mill 11 Floor 12 Side wall 13 Alumina-based refractory 14 Tundish outlet

Claims (2)

  In continuous casting of steel, the shape of the alumina refractory is fixed and installed on either or both of the side wall and the floor in the tundish, and the nonmetallic inclusions contained in the molten steel adhere to the alumina refractory. A method for removing non-metallic inclusions in molten steel.   The non-metallic inclusions in molten steel according to claim 1, wherein the non-metallic inclusions are made of alumina-based refractories containing 60% or more of alumina. How to remove.

Images