JPH0349966B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a method for increasing the temperature of molten steel in a vacuum degassing tank for degassing molten steel. (Prior art) In order to manufacture steel without internal defects, it is widely and generally practiced to perform vacuum degassing treatment on molten steel, but in this case, the temperature of molten steel decreases as the treatment time progresses, This poses a quality and operational problem. As a countermeasure to this problem, a method has been proposed as a vacuum degassing method for molten steel (Japanese Patent Publication No. 50763/1983), in which oxygen gas is blown into the side wall of the vacuum degassing tank to raise the temperature. As shown in Fig. 3, this method involves sucking up molten steel 5 in a refractory-lined ladle 4 into a vacuum degassing tank 1 in a high vacuum state, and blowing oxygen gas into the molten steel through a nozzle 3 to remove oxygen. Inside the molten steel [Al],
The temperature of molten steel is raised by heat generation with [Si]. Although this method can raise the temperature of molten steel, it has the following problems. That is, the nozzle is constantly immersed in the molten steel, and even after the oxygen injection to raise the temperature has ended, some kind of gas (hereinafter referred to as "protective gas") must be passed through the nozzle to prevent it from clogging. As a result, the cost of the protective gas increases, and as the vacuum chamber progresses to a high vacuum to degas the molten steel, molten steel scatters using the protective gas as a power source, and this adheres to the inner wall of the vacuum chamber, causing molten steel loss and adhesion. Operations have been suspended to remove metal. In order to prevent this metal from adhering, electrode heating and gas preheating within the vacuum chamber have been carried out, but both lead to increased costs and only incomplete results have been achieved. On the other hand, in order to prevent metal adhesion, the oxygen blowing nozzle in the vacuum degassing tank is installed higher than the surface of the molten steel in the tank, as shown in Figure 4, to avoid clogging of the molten steel nozzle after the oxygen blowing is completed, and to reduce the cost of protective gas. There is a method to reduce this, and this method is preferable because it reduces metal buildup in the vacuum degassing tank, but the refractories in the vacuum degassing tank are severely eroded, leading to a decrease in operating efficiency and an increase in the cost of refractories due to a shortened tank life. It's on. (Problems to be Solved by the Invention) The present invention prevents metal build-up in the vacuum degassing tank, eliminates the drawbacks of severe melting and loss of refractories, and solves the problem of molten steel by blowing oxygen gas during vacuum degassing treatment. This invention relates to a method for significantly extending the service life of a vacuum chamber and making it more advantageous to use when the temperature increases. (Means for Solving the Problems) The present invention is characterized by arranging oxygen blowing nozzles in multiple stages vertically on the inner wall of the vacuum chamber, and by sequentially switching from the upper stage to the lower stage. The purpose is to reduce erosion loss. It is said that the top blow nozzle method causes a large amount of erosion of the refractories in the RH tank, but the inventor's research shows that the rate of erosion of the refractories is not large at the beginning of use.
It was found that as the number of times the refractory was used increased, the amount of erosion of the refractory material increased rapidly. As shown in Figure 4, the cause of this is that the top blow nozzle was set according to the standard at the beginning of use, but as the refractories inside the tank were used over time, the refractories inside the tank were eroded and the top blow nozzle became short. Therefore, the oxygen blown into the molten steel is in an upward blowing state where the distance is farther away than at the beginning of use, and the blowing force of oxygen gas gradually becomes weaker as the number of times of use progresses. As a result, it was found that the stirring force of the molten steel, which is generated as the molten steel surface is heated, weakens, resulting in a local temperature rise of the molten steel surface, which causes the refractory corrosion to progress even further. The present invention focuses on this point, and in order to extend the overall life of the tank, avoid the fact that the life of the tank comes to an end relatively early due to local erosion of the refractories in the RH tank, and move the area where it is used to ensure that the refractories in the RH tank are not eroded evenly. This was achieved by making In other words, as the number of times the RH tank is used increases, the refractories inside the tank will be eroded and the top blowing nozzle will also become shorter, causing a tendency for oxygen to blow upward into the molten steel. Switch to the lower nozzle where the refractory remains relatively healthy. As a result, the amount of oxygen blown onto the molten steel is the same as when the RH tank was first used, and erosion of the refractories in the tank is also reduced. There is no particular limit to the level difference between the upper and lower nozzles, but it is usually advantageously implemented within a range of several tens of mm to about 200 mm. In this case, it is also possible to have the top blow nozzle in more stages than just two stages. Here, a brief explanation will be given based on the drawings. Figure 3 is a diagram of molten steel vacuum degassing operation using the oxygen blowing nozzle immersion method (Japanese Patent Publication No. 56-50763).
It has an oxygen blowing nozzle 3 at the bottom, and by creating a high vacuum inside the nozzle 3, the molten steel 5 in the ladle 4 is sucked up into the vacuum degassing tank. Note that 6 is a slag. FIG. 4 shows a top-blowing nozzle system in which the oxygen blowing nozzle in the vacuum degassing tank shown in FIG. 3 is attached above the surface of the molten steel sucked up, and 7 is the oxygen blowing nozzle. Fig. 1 shows the oxygen top-blowing nozzle system shown in Fig. 4 in which the nozzles on the inner wall of the tank are installed in multiple stages, upper and lower.The upper nozzle 8 is used initially, and after the refractory material has melted down, the lower nozzle is installed. By switching to lower nozzle 9, when the distance A between the nozzle tip and the molten steel surface at the start of use changes to B as a result of melting of the refractory and nozzle, by switching to the lower nozzle 9, the distance between the nozzle tip and the molten steel surface becomes C, and an appropriate value is secured. Furthermore, Fig. 2 is a diagram showing the change in the temperature raising efficiency of molten steel with the number of times the vacuum degassing tank is used.The temperature raising efficiency rapidly deteriorates after a certain point as the number of times the vacuum degassing tank is used. This shows that it is effective to switch from the upper nozzle to the lower nozzle. (Example) Next, an example of the present invention will be shown. The vacuum degassing equipment and operating conditions are shown in Table 1.

[Table] Table 2 shows the results of operating the oxygen injection nozzle using the molten steel immersion method using the equipment and operating method shown in Table 1.

[Table] During operation, sufficient preheating with CO gas was carried out to prevent metal buildup in the vacuum degassing tank. On the other hand, Table 3 shows the results of operation using a method in which the oxygen blowing nozzle was attached to the upper surface of the molten steel.

[Table] As shown above, the top blow nozzle method can significantly reduce metal adhesion inside the vacuum degassing tank compared to the immersion nozzle method, reduce the loss of molten steel, reduce equipment downtime, and reduce the amount of metal cutting personnel required. It has been found that this makes a significant contribution to industry, such as a significant reduction in Moreover, as a result of using this top-blowing method for a long time,
The lifespan of the vacuum degassing tank is longer than that of the immersion nozzle method.
It has decreased significantly. The comparison is shown in Table 4.

[Table] For this reason, as a result of various studies conducted by the present inventor, in the top-blowing nozzle method, the nozzle installed on the inner wall of the vacuum degassing tank becomes shorter due to erosion of the inner wall refractories, and as a result, the molten steel inside the tank becomes shorter. It was discovered that the oxygen blowing conditions to the surface were changing, causing severe damage to the inner wall refractories.As a countermeasure, we installed multiple nozzles above and below, moving from the upper nozzle to the lower nozzle as the damage to the inner wall progressed. It was discovered that switching to the vacuum degassing tank is effective in extending the life of the vacuum degassing tank. Table 5 shows the operation results using this top-blowing nozzle multi-stage installation method. There is no difference in the amount of metal deposited inside the tank compared to the conventional top-blowing method, and the life of the vacuum degassing tank is greatly improved, with no disadvantages due to metal adhesion. It is possible to enjoy the benefits of both avoiding the problem and extending the life of the tank.

【table】 [Brief explanation of drawings]

Figure 1 is a schematic diagram of the multi-stage oxygen top-blowing nozzle system according to the present invention, Figure 2 is a diagram showing the change in heating efficiency between the present invention and the conventional method, and Figure 3 is a diagram showing the method for raising the temperature of molten steel using a vacuum degassing tank immersion nozzle. Figure 4 shows a conventional method for raising the temperature of molten steel using a blowing nozzle above the surface of a vacuum degassing bath. 1: Vacuum degassing tank, 2: Refractory, 3: Oxygen injection nozzle, 4: Ladle, 5: Molten steel, 6: Slag,
7: Oxygen blowing nozzle, 8: Upper nozzle, 9: Lower nozzle.

Claims (1)

[Claims] 1. A method for increasing the temperature of molten steel in a vacuum degassing tank, characterized in that a plurality of nozzles that spray oxygen gas toward the bath surface in the tank are vertically arranged on the side wall of the vacuum degassing tank, and the nozzles are used in sequence from the upper nozzle. .