JP2010132980A - Method for restraining sticking of scull onto top-cover of rh vacuum-degassing vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for restraining sticking of scull onto the top-cover of RH vacuum-degassing tank, with which growth of the scull stuck on the top-cover can be restrained. <P>SOLUTION: The method for restraining formation of a stuck material caused by splash of molten steel onto the top-cover of the RH vacuum-degassing vessel, is newly disclosed. Specifically, the inner surface of the top-cover is formed in a horizontal state or in a projecting state downward by using unshaped refractories and flowing in the side-direction of the stuck material is restrained and dropped down vertically so as to prevent solidification and the growth. In this case, it is more effective when a high Cr-containing steel is used as the molten steel or Al<SB>2</SB>O<SB>3</SB>quality or Al<SB>2</SB>O<SB>3</SB>-MgO based unshaped refractories are used. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for preventing the adhesion of a metal to an RH vacuum degassing tank canopy, and more specifically, when refining molten steel discharged from a converter in an RH vacuum degassing tank, the ceiling lid (hereinafter referred to as a canopy). ) Is related to a technology that suppresses the growth of molten steel splash on a large lump of metal.

  Generally, molten steel melted by oxygen blowing in a converter is once put into a ladle and then cast by a continuous casting machine or the like to form a steel slab. This steel slab becomes a steel product after rolling and various processings. In recent years, in order to improve the quality of steel products, it is called “secondary refining”, and impurity components contained in steel slabs are further removed by adding various refining means. One of the removal methods is a technique using an RH vacuum degassing tank. The ladle containing the molten steel discharged from the converter is set in an RH vacuum degassing tank and further decarburized by oxygen blowing or degassed under reduced pressure.

Here, as shown in FIG. 2, the RH vacuum degassing tank 16 is connected to an exhaust means (not shown) and is held in a tank 1 (also referred to as a vacuum tank) having a depressurizable space and a ladle 2. The molten steel 3 is dipped into the tank 1 and sucked up by the drift-up force of the inert gas 22 separately blown into the tank 1 through the nozzle 25, or lowered to the ladle 2 to form a circulating flow 23. An ascending pipe 4 and a descending pipe 5 are included. And the side wall 6 and the canopy 7 of the tank 1 are lined with refractory bricks 8 so as to withstand high temperatures of 1700 ° C. or higher. The canopy 7 is characterized by having an arched brick stacking structure for the purpose of stably loading refractory bricks (material is MgO—Cr ₂ O ₃ refractory etc.) 8.

  By the way, when oxygen blowing of the molten steel 3 is performed in the RH vacuum degassing tank 16, as shown in FIG. 2, a fireproof in which droplets (hereinafter referred to as splash) scattered from the molten steel 3 are lined in the tank 1. It adheres to the surface of the brick 8 and forms a deposit 9 called a bare metal.

  Therefore, conventionally, a technique for removing the deposit 9 has been developed, and although not shown, the deposit 9 on the side wall 6 is attached as an attachment to the oxygen lance 10 inserted into the tank when the operation is stopped. It has become possible to cope with this problem by blowing an oxygen jet in a horizontal direction from a nozzle (not shown), and fusing and dropping.

  However, the deposit 9 that has grown in the canopy 7 has a problem because there is no sufficient countermeasure since the lance itself melts when the oxygen jet is directed upward. By the way, about 40 tons of bulk metal 9 adheres in the operation of about 1700 charges in the RH vacuum degassing tank (processing amount 330 tons per charge) mainly made of stainless steel containing Cr. . The deposit 9 not only reduces the yield of the molten steel 3 but also drops the refractory bricks 8 when dropped and impurities such as carbon in the deposit 9 are picked up into the molten steel 3 where secondary refining has been completed. This also causes the concentration to increase again. In addition, since the exhaust port 12 is blocked and the decompression is disturbed, the operation itself becomes difficult.

  Therefore, at present, after operating for a certain period of time, the canopy 7 is removed from the tank 1, and as shown in FIG. 3, a plurality of through-holes 13 are opened by dissolving in a lump of bulk metal (attachment 9) with an oxygen jet, The wire 14 is passed through the through-hole 13 and lifted by a crane (not shown) and lowered to remove the ingot 9 from the tank 1 (in FIG. 3, the canopy 7 has not been removed yet). However, such a removal operation takes a long time, and not only the productivity of the molten steel using the RH vacuum degassing tank is lowered, but when this operation is actually performed, FIG. 4 (a) and FIG. As shown in (b), there was always a danger that the operator 15 was burned or the wire 14 was cut.

The canopy 7 of the RH vacuum degassing tank 16 has an arch shape as described above. However, in the documents (including patent publications) disclosed so far, the canopy 7 is schematically shown as a horizontal shape in the attached drawings. (For example, refer to Patent Document 1), such a horizontal shape does not exist for the convenience of brickwork.
JP 62-148551 A

  In view of such circumstances, an object of the present invention is to provide a method for suppressing the adhesion of an ingot to an RH vacuum degassing tank canopy that can suppress the growth of the ingot attached to the canopy.

  The inventor has intensively studied to achieve the above object, and the results have been embodied in the present invention. That is, the present invention uses an RH vacuum degassing, wherein the canopy of the RH vacuum degassing tank is one in which the inner surface of the canopy is formed horizontally or downward using an irregular refractory. This is a method for suppressing metal adhesion to the tank canopy.

In this case, the molten steel is preferably made of high Cr content steel, or the amorphous refractory is made of high Al ₂ O ₃ or Al ₂ O ₃ —MgO.

  In the present invention, the inner surface of the canopy of the RH vacuum degassing tank is formed horizontally or downwardly using an irregular refractory. As a result, the adhering matter is restrained from flowing in the lateral direction and immediately drops vertically, thereby preventing solidification and growth at the adhering position. Therefore, not only the frequency of dangerous work for the operator is reduced, but also the damage of the refractory due to the collapse of the metal, the pickup of carbon can be reduced, and the improvement of the molten steel yield can be achieved.

  Hereinafter, the best embodiment of the present invention will be described based on the background of the invention.

  First, the inventor observed the situation where the adhesion metal grew and spread in the arch of the canopy 7 every time one charge operation was completed. And when removing the bulk metal 9 (see FIG. 3 and FIG. 4), considering that the canopy 7 can be removed from the tank 1 relatively easily, the bulk metal 9 is a fireproof brick of the canopy 7. 8 itself did not adhere so strongly, and it was estimated that the base was on the upper end side of the side wall 6. Furthermore, the reason why the bulk metal 9 is formed is that the shape of the canopy 7 is arched, or the adhering material 9 attached to the central part of the inner surface of the canopy flows in the boundary direction between the side wall 6 and the canopy 7. It was thought that it finally went to the upper end of the side wall 6 and was enlarged and became a lump.

  Subsequently, the inventor examined measures for suppressing the growth of the deposit 9 based on the above consideration. As a result, as shown in FIG. 1, the anchor 17 is attached to the inner surface side of the iron skin 18 forming the canopy 7 of the RH vacuum degassing tank 16, the amorphous refractory 17 is filled, and the inner surface 24 is horizontally disposed. Or, I thought that it would be better to form a convex shape below. This is because it can be expected that the melt 20 adhering to the horizontal or downwardly convex surface immediately becomes a droplet 21 due to gravity and drops vertically downward rather than flowing in the lateral direction. . That is, even if it adheres to the inner refractory surface of the canopy 7 due to scattering, if the attachment position is horizontal or convex downward, it does not stay at that position, but rather falls immediately by its own weight. It should not flow and accumulate, and solidification / growth will be hindered and it will be difficult to become a deposit.

  In addition, the material of the refractory material 17 is the non-standard refractory material 17 because it is difficult to prevent the refractory brick 8 from falling from the canopy 7 in use if the refractory brick 8 is constructed horizontally. If so, a large number of anchors 19 are welded to the iron skin 18 of the canopy 7, and the refractory material is applied to the anchors 19 to prevent the fall.

Further, in the present invention, it is preferable that the operation is performed with ordinary steel and Cr-containing steel, and the amorphous refractory 17 is made of high Al ₂ O ₃ or Al ₂ O ₃ —MgO system. Even in ordinary steel and Cr-containing steel, in vacuum degassing of low alloy steel with a Cr content of 3% by mass or less, the remarkable adhesion of metal to the canopy 7 is observed as described above. It is rare. This is because even if the metal that adheres to the inner surface of the RH vacuum degassing tank 16 is a metal at the time of attachment, after the refining is finished and the molten steel is discharged into the ladle, the inside of the tank is exposed to the atmosphere. Some of them are oxidized to oxides, but the oxides are mainly iron oxides, so the melting point is lower than the melting point of the metal itself.

  When the metal is attached to the inside of the RH vacuum degassing tank 16 to some extent, the oxygen lance 10 or the burner lance is usually inserted from the canopy 7 and the tank is heated to dissolve and remove the metal. At this time, the inner surface of the canopy 7 also receives a radiant heat from the heated side wall and becomes a high temperature, and both the metal and iron oxide attached thereto can be dissolved and removed. However, there is a limit to dissolution and removal due to heat dissipation from the entire iron skin of the canopy 7.

  Particularly, in the case of refractory steel and stainless steel containing 9 mass% or more of Cr, the oxide generated when the attached metal is exposed to the atmosphere is mainly Cr oxide, and the oxide of Cr has a melting point. Is extremely high temperature of 2000 ° C or higher, so even if the metal on the side wall that directly receives the oxygen jet from the lance can be dissolved, the deposit on the canopy that is indirectly heated by the radiant heat from it cannot be easily dissolved. . For this reason, even with refractory steel and stainless steel containing 9 mass% or more of Cr, even if an oxygen lance or burner lance is inserted into the tank and the tank is heated to perform the metal melting operation, the metal attached to the side wall However, the bullion attached to the canopy 7 is not removed, and enlargement is repeated as the number of refining charges increases.

  The present invention is an RH vacuum that refines high Cr-containing steel containing 9% by mass or more of Cr, in which it is difficult to completely remove the adhered metal from the canopy 7 by such normal metal melting work. It can be particularly suitably used for a degassing tank. A composition having a Cr content of more than 3% by mass and less than 9% by mass is not practically mass-produced using the RH vacuum degassing tank 16 because its practicality as steel is poor.

  In order to confirm the above-described effects of the present invention, a so-called “secondary refining” operation in which decarburization is performed using an RH vacuum degassing tank 16 for a low carbon stainless steel containing 13 mass% Cr over 3 months. And compared with the data at the time of operation by the conventional method. Main components other than iron of the molten steel 3 after secondary refining are Cr: 13 mass%, C: 0.02 mass%, P: 0.015 mass%, and S: 0.008 mass%.

First, 330 tons of the molten stainless steel 3 is discharged from a converter (not shown) to the ladle 2, the ladle 2 is set in the RH vacuum degassing tank 16 shown in FIG. 1, and the present invention is applied. Operated. The main operating conditions are: the temperature of the molten stainless steel 3 before oxygen blowing is 1700 ° C., the oxygen blowing flow rate for decarburization from the upper blowing lance is 10 to 30 m ³ (standard state) / min, the blowing time is 30 minutes, and the blowing is completed. The deoxidizer added later was metallic aluminum. The canopy 7 is an amorphous refractory 17 made of high Al ₂ O ₃ or Al ₂ O ₃ —MgO based on the material according to the present invention. It was made to become.

  After the operation of each charge (one heat) was completed, the state of scattered matter adhering to the canopy 7 was always observed, and the presence or absence of the bulk metal 9 was confirmed. As a result, no deposits 9 were observed on the canopy 7 even after 1500 charge refining, confirming that the present invention is very effective. On the other hand, in the operation used for the RH vacuum degassing tank 16 provided with the conventional arched canopy 7, formation of the bulk metal 9 of 10 tons after the refining process of 500 charges and 40 tons after the refining process of 1500 charges. was there.

  That is, the use of the present invention not only reduces the frequency of dangerous work for the operator, but also can reduce refractory damage and carbon pick-up due to collapse of the metal, and can be expected to improve the molten steel yield. .

It is the figure which expanded and showed typically the upper part of the RH vacuum degassing tank utilized for implementation of this invention. It is a schematic diagram which shows the operation condition in the RH vacuum degassing tank provided with the conventional arch type canopy. It is a schematic diagram explaining the removal operation | work of a block metal. It is a figure explaining the danger which arises in the removal operation | work of the said lump metal, (a) is fear of a burn by an operator's hot air, (b) expresses the danger of wire cutting.

Explanation of symbols

1 tank 2 ladle 3 molten steel (stainless steel)
4 Climbing pipe 5 Climbing pipe 6 Side wall 7 Canopy 8 Refractory brick 9 Deposits (bulk metal)
DESCRIPTION OF SYMBOLS 10 Oxygen lance 11 Oxygen jet 12 Exhaust port 13 Through-hole 14 Wire 15 Worker 16 RH vacuum degassing tank 17 Indeterminate refractory 18 Iron skin 19 Anchor 20 Melt 21 Droplet 22 Inert gas 23 Circulating flow 24 Inner surface 25 Inert gas blowing nozzle

Claims (3)

  As a canopy for the RH vacuum degassing tank, a metal bar for the RH vacuum degassing tank canopy, wherein the inner surface of the canopy is formed horizontally or downward using an irregular refractory. Adhesion suppression method.   The method for suppressing adhesion of metal to the RH vacuum degassing tank canopy according to claim 1, wherein the molten steel is high Cr-containing steel. The method for suppressing adhesion of a metal to an RH vacuum degassing tank canopy according to claim 1 or 2, wherein the amorphous refractory is made of high Al ₂ O ₃ or Al ₂ O ₃ -MgO.

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