JP2012180559A - Degassing method of molten steel using circulating vacuum chamber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further extend the life of a dip tube while reducing trouble such as vacuum failure or suction of slag without increase in refractory thickness in vacuum degassing of molten steel using a circulating vacuum chamber.SOLUTION: When a gas component in molten steel is removed by immersing dip tubes 5, 6 provided in a vacuum chamber in the molten steel stored in a ladle 7 and circulating the molten steel between the vacuum chamber and the ladle 7 while maintaining the dipping depth of the dip tubes 5, 6 by moving up and down the ladle, the level of slag surface in the ladle 7 is measured by a microwave level meter 8 during the circulation of the molten steel, and based on this measurement result, the distance L between the lower end surfaces of attachment flanges of the dip tubes and the slag surface of the slag in the ladle is maintained in the range of 100-200 mm.

Description

  The present invention relates to a method for degassing molten steel using a reflux vacuum tank, and intends to extend the life of a dip tube provided in the vacuum tank without causing operational troubles.

  The main purpose of the vacuum degassing process for molten steel is to remove gas components (hydrogen, nitrogen, etc.) in the molten steel, to adjust the molten steel components by adding alloyed iron, and to equalize the temperature.

  In the vacuum degassing process, conventionally, a reflux-type vacuum tank having two dip pipes connected via a flange is used, and the slag surface level in the ladle containing the molten steel is the dip of the slag surface. An operator visually raises and lowers the position of the ladle so as to be maintained just below the flange connecting the pipes.

  By the way, in the said dip tube, the melting loss of the flange was intense, and it became one of the rate limiting of dip tube life and repair.

  The reason why the slag surface level is maintained directly below the flange is as follows.

  The flange is a part where the joining surface of the dip tube and the vacuum chamber is formed. Usually, an O-ring is disposed between the flanges as a sealing member for improving the airtightness, but this part is immersed in the slag. If this happens, the O-ring will burn out, making it difficult to maintain a high vacuum (vacuum failure).

  In addition, when the lower end of the dip tube is located in the slag existing area, suction of the slag into the vacuum chamber causes troubles such as blockage of the exhaust port, and the degassing treatment cannot be performed, thereby hindering the operation. It will end up.

  As a conventional technique for solving the problems as described above, the measurement disclosed in Patent Document 1 is to accurately grasp the steel bath height in the vacuum layer by monitoring the slag surface level with a microwave level meter. The device is known.

  In addition, as a prior art similar to this, in Patent Document 2, when the molten metal surface level in the ladle suddenly fluctuates, or when the slag thickness is not uniform, the variation of the slag surface level is synchronized with the variation of the molten metal surface level. There has been proposed a method and apparatus for adjusting the immersion depth of the dip tube with high accuracy even in the absence of the dip tube. Further, Patent Document 3 discloses a hot water surface monitoring camera for the gap between the bottom surface of the dip tube and the slag surface. Observed in, detecting the contact between the bottom surface of the dip tube and the slag surface, the level of the hot water level obtained by subtracting the slag thickness detected in advance from the level of the slag surface at the time of contact, There has been proposed a method and an apparatus in which the immersion depth of the dip tube is adjusted.

JP 2006-249502 A Japanese Patent Laid-Open No. 11-323427 Japanese Patent Laying-Open No. 2005-2391

  By the way, in the above-mentioned patent documents 1 to 3, although a certain degree of effect can be expected in terms of eliminating troubles such as vacuum failure due to O-ring burnout and exhaust port blockage, the contact portion of the dip tube with the slag At present, it cannot be said that sufficient studies have been made to extend the life of the dip tube by suppressing the melting loss of the dip tube.

  In order to extend the life of the dip tube, it is effective to increase the thickness of the refractory (brick) at the contact portion of the slag, but simply increasing the thickness of the refractory only There is a defect that leads to cost increase.

  The present invention is a reflux which can further extend the life of the dip tube while suppressing troubles such as vacuum failure and slag suction during vacuum degassing treatment without increasing the thickness of the refractory. It aims at proposing the degassing processing method of the molten steel using a vacuum-type vacuum chamber.

In the present invention, a dip tube provided in a vacuum tank is immersed in molten steel accommodated in a ladle, and the immersion depth of the dip tube is kept constant by moving the ladle up and down. In removing the gas component in the molten steel by refluxing the molten steel between the tank and the ladle,
While the molten steel is refluxed, the level of the slag surface in the ladle is measured by a level meter. Based on the measurement result, the bottom of the mounting flange of the dip tube reaches the slag surface of the slag in the ladle. This is a method for degassing a molten steel using a reflux vacuum tank, characterized in that the distance is maintained in the range of 100 to 200 mm.

  In the present invention, it is desirable to change the distance step by step for each processing charge. As the level meter, a microwave level meter can be used.

  By moving the ladle up and down and maintaining the distance from the lower end surface of the mounting flange of the dip tube to the slag surface of the slag in the ladle within the range of 100 to 200 mm, the melting of the flange is suppressed. At the same time, the generation and growth of deposits (attachments mainly composed of slag) at the tip of the dip tube are suppressed.

  In addition, by changing the distance stepwise within a range of 100 to 200 mm for each processing charge, it becomes possible to appropriately change the erosion site of the dip tube (dispersion of the erosion site). As a result, the life of the dip tube is extended.

It is the figure which showed typically the reflux-type vacuum degassing tank suitable for implementing the degassing processing method according to this invention with the ladle. It is the figure which expanded and showed the dip tube of the reflux-type degassing tank shown in FIG.

Hereinafter, the present invention will be described more specifically with reference to the drawings.
FIG. 1 is a view schematically showing a reflux type vacuum vessel suitable for use in carrying out the present invention together with a ladle, and FIG. 2 shows a main part of the reflux type vacuum vessel shown in FIG. It is the figure expanded and shown.

  Reference numeral 1 in the figure denotes a vacuum chamber body formed by using a steel plate as a skin and lining a heat-resistant material such as a brick on the skin. The vacuum chamber body 1 is provided at a cylindrical body 1a, an upper end of the body 1a, a top plate 1b that forms a ceiling of the vacuum body 1, and a lower end of the body 1a. It is comprised from the baseplate 1c which forms the bottom wall of the vacuum chamber main body 1. FIG. An inner region surrounded by the body 1a, the top plate 1b, and the bottom plate 1c of the vacuum chamber body 1 is a molten steel degassing space M.

  Further, 2 is an exhaust duct provided on the upper portion of the body portion 1a of the vacuum chamber body 1 and having a passage leading to the degassing processing space M, and 3 and 4 are provided at intervals on the bottom plate 1c of the vacuum chamber body 1. Reflux tube. At the lower ends of the reflux pipes 3 and 4, flanges 3a and 4a are formed.

  5 is a dip tube (suction tube) immersed in the molten steel in the ladle, and 6 is a dip tube (discharge tube) immersed in the molten steel in the ladle. The dip tubes 5 and 6 have flanges 5a and 6a formed at their upper ends.

  The flanges 5a and 6a of the dip tubes 5 and 6 and the flanges 3a and 4a of the reflux tubes 3 and 4 can abut each other, and the dip tubes 5 and 6 and the reflux tube 3 The dip tubes 5 and 6 are fixedly held on the bottom plate 1c of the vacuum chamber body 1 by abutting 4 and connecting them together by fastening means such as bolts.

  7 is a ladle which accommodates the molten steel which should be degassed. The ladle 7 is provided with a drive mechanism that can be moved up and down by automatic operation as appropriate, although a specific structure is not shown.

  Reference numeral 8 denotes a microwave level meter that is provided on the outer surface of the body 1a of the vacuum tank body 1 and constantly measures the slag surface level in the ladle 7.

  The result measured by the microwave level meter 8 is transmitted to the control system that controls the drive mechanism as needed, and from the lower end surface of the dip tubes 5 and 6 to the slag surface of the slag in the ladle as shown in FIG. The ladle 7 is appropriately moved up and down so that the distance L is kept constant within a range of 100 to 200 mm. Here, although the case where the microwave level meter 8 is provided in the present invention to measure the distance L has been described, other measuring means can also be used.

  In order to perform the degassing treatment of the molten steel using the vacuum tank having the above-described configuration, first, the molten steel produced from the converter or the like is accommodated in the ladle 7, and then the ladle 7 is placed in the vacuum tank body 1. Then, the ladle 7 is raised and the dip tubes 5 and 6 fixed and held on the bottom plate 1c of the vacuum chamber body 1 are immersed in the molten steel in the ladle 7 at a predetermined depth.

  The vacuum tank body 1 is depressurized and the molten steel in the ladle 7 is sucked into the processing space M through the dip tube 5, while the molten steel sucked up in the processing space M is discharged to the ladle 7 through the dip tube 6. The operation to be repeated is repeated a plurality of times (at this time, the ladle 7 is appropriately controlled to move up and down so that a predetermined immersion depth is maintained). Due to the sucking and discharging, the molten steel is refluxed between the vacuum chamber main body 1 and the ladle 7, and gas components (oxygen, hydrogen, etc.) in the molten steel are removed in the degassing treatment space M.

  In the present invention, in particular, the distance L from the lower end surface of the mounting flange of the dip tube to the slag surface of the slag in the ladle is maintained in the range of 100 to 200 mm, because the distance L If the distance L is less than 100 mm, the flanges 3a, 4a, 5a, 6a are too close to the ladle slag, so that the portion is severely melted. This is because, of the pipes 5 and 6, the growth of deposits (deposits mainly composed of slag) generated at the tip of the downcomer pipe side where the molten steel falls tends to be promoted. In particular, when the growth of the deposit is promoted at the tip (lower end) of the downcomer pipe among the dip tubes 5 and 6, the deposit is accompanied with the reflux process when the molten steel is degassed and the ladle 7 is moved up and down. This is because there is a concern that the detachment from the dip tube disperses in the steel and the cleanliness of the molten steel decreases.

  For this reason, in this invention, we decided to hold | maintain the distance L to the slag surface of the slag in a ladle in the range of 100-200 mm.

  The above distance L is basically kept constant within a range of 100 to 200 mm, but it is preferable to change the distance stepwise within the range for each processing charge. , 6 melting ranges are dispersed, and the life of the dip tubes 5 and 6 is extended. The change of the distance L may lower the ladle 7 or may include a level-up stage in the meantime, and this point is not particularly limited. The dip tube has typical dimensions of an inner diameter of 400 to 750 mm, an outer diameter of 1000 to 1300 mm, and a length under the flange of 570 to 700 mm, but can be applied to any dip tube.

  Using a reflux-type vacuum degassing tank (RH degassing tank) equipped with dip tubes 5 and 6 having an inner diameter of 500 mm, an outer diameter of 1100 mm, and a length (length from the mounting flange to the tip) of 620 mm, the following Investigation of degassing treatment of molten steel (steel type: low carbon steel (carbon content of 0.2% by mass or less)) contained in ladle under conditions, and dip tube life (dip tube repair frequency index) In the degassing process, the level of slag in the ladle is constantly monitored by a microwave level meter, and the ladle position is adjusted (ascending and descending) by automatic operation so that the distance L is kept constant. went.

Operating conditions of comparative example 150 mm fixed from the lower end of the mounting flange of the dip tube and repaired with 300 charges Operating conditions of the inventive example 300 t ladle used, number of charges: 600 times Distance L: 1-100 charges 200 mm, 101-200 150mm charge,
201-300 charge 100mm, 301-400 charge 200mm,
401-500 charge 150mm, 501-600 charge 100mm,

  As a result, when the repair frequency in the degassing operation according to the conventional method (comparative example) (the immersion depth of the dip tube is constant 150 mm) is 1.0, the repair frequency is 0.5 in the operation according to the present invention. As a result, it was confirmed that the life of the dip tube can be extended to about twice that of the conventional case.

  In addition, when the distance L was changed to 50 mm, 250 mm, and 300 mm and the degassing treatment was performed, the life of the dip tube was investigated. It was melted and the dip tube was repaired three times more frequently. When the distance L is set to 250 mm and 300 mm, there is no particular problem with the fusing damage of the flange, but the deposit is dispersed in the steel by promoting the growth of the deposit generated at the tip of the dip tube. It became clear that the coarse inclusions in the steel may be generated, and the longer the distance L, the higher the rate of contamination of the molten steel.

  According to the present invention, it is possible to suppress troubles such as vacuum failure and slag inhalation during vacuum degassing without increasing the thickness of the refractory, and to further extend the life of the dip tube. became.

DESCRIPTION OF SYMBOLS 1 Vacuum tank main body 1a Body part 1b Top plate 1c Bottom plate 2 Exhaust duct 3 Reflux pipe 3a Flange 4 Reflux pipe 4a Flange 5 Immersion pipe 5a Flange 6 Immersion pipe 6a Flange 7 Ladle 8 Microwave level meter M Degassing processing space

Claims (3)

A dip tube provided in a vacuum vessel is immersed in molten steel contained in a ladle, and the immersion depth of the dip tube is kept constant by moving the ladle up and down, while the vacuum vessel and the take-up tube are kept constant. In removing the gas component in the molten steel by refluxing the molten steel between the pots,
While the molten steel is refluxed, the level of the slag surface in the ladle is measured by a level meter. Based on the measurement result, the bottom of the mounting flange of the dip tube reaches the slag surface of the slag in the ladle. Is maintained in the range of 100 to 200 mm. A degassing method for molten steel using a reflux vacuum tank.   The method for degassing molten steel using the reflux vacuum tank according to claim 1, wherein the distance is changed for each processing charge.   The method for degassing molten steel using a reflux vacuum tank according to claim 1 or 2, wherein a microwave level meter is used as the level meter.

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