JP2007326116A - Continuous casting method to prevent contamination sources from entering tundish - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously cast clean steel without pouring nonmetallic inclusions into a tundish by adopting a method replaced with a conventional preliminary cutting when pouring from a ladle into a tundish with a long nozzle.
When pouring molten steel into a tundish from a ladle 1 having a sliding nozzle 2 comprising a long nozzle 2a, a hot water pot 5 is disposed in the tundish 4 in advance, and the chromium in the long nozzle 4 is disposed. After opening the padding made of sand 6, the molten steel containing the padding made of chrome sand 6 is received by the tundish 4 from the sliding nozzle 2a into the hot water pot 5, and then the sliding nozzle 4 is once closed, After removing the hot water pot 5 that has received the molten steel containing the filling from the tundish 4, the sliding nozzle 4 is opened again to pour the molten steel into the tundish 4, and clean steel is continuously cast.
[Selection] Figure 1

Description

  The present invention relates to the production of high cleanliness steel in continuous casting, and in particular to the injection of molten metal from a ladle into a tundish.

  For example, steel materials for automobile parts such as CVJ and CVT that are used under harsh conditions and require durability are required to be high cleanliness steel containing as little non-metallic inclusions as possible to impede durability. . In the production of such high cleanliness steel, conventionally, high melting by electric furnace refining has been carried out, and subsequent non-metallic inclusions in the molten steel have been refined by ladle refining and vacuum degassing, and from the molten steel. Non-metallic inclusions are reduced as much as possible. In order to continuously cast molten steel with high cleanliness in this way, pouring from the ladle to the tundish, pouring from the tundish to the mold for continuous casting, and further pulling out from the continuous casting machine, such as bloom The solidification rate is controlled to obtain as clean a slab as possible.

  However, when the molten steel melted with high cleanliness is treated with a ladle, non-metallic inclusions may be mixed into the molten steel from the slag or furnace wall on the ladle molten steel. Silica sand, nail or silica sand and chrome oxide (hereinafter collectively referred to as “chrome sand”), which are fillings in the ladle sliding nozzle, are mixed in at the beginning of pouring. Thus, if the contamination source which consists of a nonmetallic inclusion is mixed in molten steel when pouring molten steel from a ladle to a tundish, it will further enter the mold for continuous casting from a tundish.

  On the other hand, the sliding nozzle, which is usually the pouring hole at the bottom of the ladle furnace, is closed with chrome sand filling, but this chrome sand is used when pouring molten steel that has been degassed or refined from the ladle to the tundish. Open the sliding nozzle closed as it is or fill it with small iron scraps and heat it with oxygen or oxygen and combustible gas to pour molten steel into the tundish. In these opening operations, contamination sources such as stuffed chrome sand and oxidized small iron scraps are dropped into the tundish, and further mixed into the mold at the beginning of casting by the molten steel flow from the ladle and are not contained in the slab. It becomes a metal inclusion source.

  Chromium sand containing natural oxides when opening the sliding nozzle and chromium sand containing lower oxides such as iron oxide by forced opening are reduced by highly reducing elements such as Al in the tundish. As a result, non-metallic inclusions such as alumina are generated, and the non-metallic inclusions are contained in the steel, resulting in product defects, resulting in a reduction in the mechanical life of the product. Further, in continuous casting, the amount of the above-mentioned contamination source oxide accumulated in the tundish as casting progresses increases, and the cleanliness of the molten steel is further deteriorated.

  Therefore, as described above, when the molten steel is poured from the ladle 1 to the tundish 4 as shown in FIG. The stuffing of the sliding nozzle 2 such as the chrome sand 6 and the initial molten steel mixed in the slag are received in the hot water pot 5 installed outside the tundish 4, and the contamination source such as the chrome sand 6 is mixed into the tundish 4 from the ladle 1. By preventing this, a method has been developed in which non-metallic inclusions are not mixed into a slab by continuous casting (for example, see Patent Document 1). In this case, the sliding nozzle 2 of the ladle is a conventional nozzle having a normal length.

  In this method, when pouring molten steel from the ladle 1 to the tundish 4, the sliding nozzle 2 of the ladle 1 is opened, and the initial molten metal from the ladle 1 containing chrome sand and iron oxide as nozzle fillings. Is preliminarily cut and received in a hot water pot 5 provided outside the tundish 4, then the sliding nozzle 4 is made into a semi-open hole, and the leaked molten steel is transferred from the hot water pot 5 to the tundish 4, and then the sliding nozzle 2 Is fully opened and molten steel is poured from the ladle 1 into the tundish 4.

  However, when the sliding nozzle 2 used when pouring from the ladle 1 to the tundish 4 is the long nozzle 2a, the long nozzle 2a enters the tundish 4 due to the long nozzle structure. Therefore, the tip of the long nozzle 2a cannot be connected to the trough 3 for discharging out of the tundish. In other words, preliminary cutting cannot be performed from the ladle 1 directly above the tundish 4 to the hot water pot 5 outside the tundish 4 via the basket 3. Therefore, as shown in FIG. 3, in the case of the long nozzle 2a, the hot water is poured as it is from the ladle 1 into the tundish 4 without preliminary cutting. However, in this case, non-metallic inclusions such as chrome sand filling the long nozzle 2a of the ladle 1 enter the tundish 4 from the ladle 1 at the beginning of pouring, and the resulting continuous cast slab The cleanliness of was getting worse.

JP 2003-285143 A

  The problem to be solved by the present invention is that, as described above, when the nozzle used for pouring from the ladle to the tundish is a long nozzle, pre-cutting of molten steel cannot be performed when pouring from the structure. By replacing the conventional pre-cutting method, clean steel is continuously cast without filling the tundish with non-metallic inclusions such as iron oxide and other fillers such as chrome sand in the long nozzle at the beginning of pouring. Is to provide a way to do.

  Means of the present invention for solving the above problems will be described. First, at the start of pouring from a sliding nozzle consisting of a ladle long nozzle, a hot water pot in a separate container prepared in advance is placed in the tundish, and the initial molten steel is received together with a pad of chrome sand. Is removed from the tundish and pouring is started again in the tundish. In this case, the amount of molten steel including the stuffing of chrome sand injected from the long nozzle at the beginning of pouring is grasped in advance, and a hot water pot corresponding to the amount is prepared. By the way, in the above pouring, the chrome sand of the filling dropped into the tundish at the beginning of opening of the long nozzle produces non-metallic inclusions such as alumina reduced by a highly reducing element such as Al. This non-metallic inclusion causes a product defect. Further, as continuous casting progresses, these non-metallic inclusions are accumulated in the tundish, and the cleanliness of the molten steel poured into the tundish is further deteriorated. This method accepts and removes these non-metallic inclusions in a separate hot water pot provided in the tundish as described above, so that the molten steel poured into the tundish is contaminated with non-metallic inclusions. This is a method for preventing the occurrence of the problem.

  That is, when the molten steel is poured into the tundish from the ladle having the sliding nozzle composed of the long nozzle, the means of the invention of claim 1 is arranged in advance with a hot water pot in the tundish, After opening padding made of chrome sand such as silica sand or silica sand and chrome oxide, open the sliding nozzle, accept molten steel containing padding made of chrome sand etc. in a hot water pot, and once close the sliding nozzle, After removing the hot water pot that received the molten steel containing the chrome sand filling from the tundish, open the sliding nozzle again and pour the molten steel into the tundish, to the tundish of the pollution source caused by the nozzle filling This is a continuous casting method for preventing the contamination of the steel.

  By doing in this way, in a state where the ladle is arranged on the tundish, it is possible to accept molten steel containing padding made of chrome sand etc. in the hot water pot, and it is only necessary to move the hot water pot, Efficiency is good.

  According to a second aspect of the present invention, the hot water pot disposed in the tundish is preliminarily provided with an amount of molten steel containing chrome sand of filling material poured from the long nozzle into the hot water pot in the initial stage of pouring from the ladle. The continuous casting method for preventing contamination of the tundish from the contamination source caused by the nozzle filling of the means of claim 1, characterized by comprising the capacity obtained by grasping.

  If the size of the hot water pot is determined in advance as described above, the amount of the initial contamination source cut out from the ladle can be easily set, and the efficiency is increased because unnecessary cutting is not performed.

  By using the means of the present invention, in the pouring from the ladle having a long nozzle to the tundish, the non-metallic inclusions formed from the filling of the nozzle are eliminated, and the high-cleanness is eliminated. The method of the present invention is unprecedented in that it can continuously cast a slab of high-grade steel, and when this slab is manufactured into a product such as an automobile part, a highly durable and highly clean product can be easily manufactured. It has an excellent effect.

  The best mode of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a preliminary cutting method when pouring into a tundish from a ladle having a long nozzle in the method of the present invention. FIG. 2 is a diagram illustrating a conventional preliminary cutting method outside the tundish. FIG. 3 is a diagram showing a method of pouring directly into a tundish from a ladle having a long nozzle without preliminary cutting.

  When the pouring from the sliding nozzle 2 having the long nozzle 2 a of the ladle 1 to the tundish 4 is started, a hot water pot 5, which is a separate container prepared in advance, is disposed in the tundish 4. The height of the hot water pot 5 is set so that the tip of the long nozzle 2 a of the ladle 1 does not enter the hot water pot 5 when the hot water pot 5 is disposed in the tundish 4. Removable height. When the hot water pot 5 is arranged in the tundish 4 as described above, the initial molten steel is received from the ladle 1 together with the stuffing of the chrome sand 6 into the hot water pot 5, and the hot water pot 5 is removed from the tundish 4 to the outside. After that, the pouring of the tundish 4 from the ladle 1 is started again.

  In this case, at the initial stage of pouring of molten steel containing the stuffing of chrome sand 6, the amount of molten steel containing the stuffing of chrome sand 6 injected from the long nozzle 2 a is grasped in advance, and the capacity corresponding to the amount is filled. A waste water pot 5 is prepared and installed in the tundish 4. By the way, in the above pouring, the chrome sand 6 of the filling dropped into the tundish 4 at the beginning of opening of the long nozzle 2a is a non-metallic inclusion such as alumina reduced by a highly reducing element such as Al. This non-metallic inclusion causes a product defect. Further, as the continuous casting of the continuous casting proceeds, these non-metallic inclusions are accumulated in the tundish 4, and the cleanliness of the molten steel poured into the tundish 4 is further deteriorated. In the method of the present invention, these non-metallic inclusions are received and removed in advance in a separate hot water pot 5 provided in the tundish 4 as described above, so that the molten steel poured into the tundish 4 can be removed. Prevent contamination by metal inclusions.

  JIS G 4805 high carbon bearing steel grade SUJ2 is melted in an electric furnace, smelted in a ladle furnace and refined in the usual manner. The refined molten steel is poured from the ladle 1 into the tundish 4 and continuously. Casted. The cleanliness of the molten steel in the tundish 4 by these methods is shown in Table 1 below. In Table 1, heat No. 1 and 2 show the method according to the method of the present invention shown in FIG. 1, and precut into the hot water pot 5 in the tundish 4. Heat No. Nos. 3 and 4 show a method of preliminary cutting outside the tundish by the conventional normal nozzle shown in FIG. 2, and the ladle 1 is poured while sequentially rotating on the swing tower 7 as shown in FIG. So you can pour one after another. Heat No. Nos. 5 and 6 show a method of pouring directly into the tundish 4 without preliminary cutting with the conventional long nozzle shown in FIG.

  In Table 1, the cleanness index is obtained by indexing the number of non-metallic inclusions in a unit volume over a certain size in the conventional method of pouring directly into the tundish 4 without preliminary cutting shown in FIG. The average value of the 100 heats is 10, and this is used as a standard for the cleanliness level. A smaller index indicates a higher cleanliness. In the method of the present invention, heat no. 1 with an index of 8.2, heat no. The index was 2 and the index was 7.7. On the other hand, in the method of preliminary cutting outside the tundish of the conventional method shown in FIG. 3 with an index of 7.7, heat no. The index was 4 and the index was 7.9. On the other hand, in the method of pouring directly into the tundish without the preliminary cutting of the conventional method shown in FIG. 5 with an index of 9.3, heat no. The index was 6 and the index was 9.4, and the chrome sand 6 entered the tundish 4 at the beginning of the injection to deteriorate the cleanliness.

  As described above, in the method shown in FIG. 1 of the present invention, the molten steel containing the chrome sand 6 is received in the hot water pot 5 disposed in the tundish 4 at the beginning of pouring from the ladle 1 into the tundish 4 and removed in advance. Even if the method uses the long nozzle 2a, the hot water pot 5 is disposed in the tundish 4 in this way, and the initial molten metal from the ladle 1 is preliminarily cut into the hot water pot 5. 2 was almost the same as the precutting method outside the tundish shown in FIG. 2 and was not inferior. Therefore, the molten steel of the tundish 4 was sufficiently clean.

It is a figure which shows the preliminary cutting method at the time of the pouring to the tundish from the ladle which has a long nozzle in the method of this invention. It is a figure which shows the preliminary cutting method out of the conventional tundish. It is a figure which shows the method of pouring directly into a tundish from the ladle which has a long nozzle, without preliminary cutting.

Explanation of symbols

1 Ladle 2 Sliding nozzle 2a Long nozzle 3 ノ ズ ル 4 Tundish 5 Waste water pot 6 Chrome sand 7 Swing tower

Claims (2)

  When pouring molten steel into a tundish from a ladle having a sliding nozzle consisting of a long nozzle, a hot water pot is placed in the tundish in advance, and a chrome sand such as quartz sand or quartz sand and chrome oxide in the long nozzle. The sliding nozzle is opened and the molten steel containing the chrome sand filling is received in the hot water pot. After the sliding nozzle is closed, the molten steel containing the chrome sand filling is received. After removing the hot water pot from the tundish, the sliding nozzle is opened again, and molten steel is poured into the tundish. A continuous casting method for preventing contamination of the tundish due to nozzle filling.   The hot water pot placed in the tundish has a large capacity obtained by grasping in advance the amount of molten steel containing chromium sand in the filling material poured into the hot water pot from the long nozzle in the initial stage of pouring from the ladle. A continuous casting method for preventing contamination of a tundish from a contamination source caused by the nozzle filling according to claim 1.

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