JPS626725B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for hot repair of a molten steel degassing immersion tube, and particularly to a method for hot repair that is easy to work with and can reduce costs. Vacuum degassing equipment such as the RH type and DH type sucks up the molten steel 4 in the ladle 2 into the degassing tank 8 through the immersion pipe 6 to perform degassing refining, as shown in the attached drawing. , the dip tube 6 is severely eroded by the slag 10 floating in the molten steel 4 in the ladle 2. Conventionally, a dip tube 6 eroded by slag 10
Common hot repair methods include spraying repair methods, pounding repair methods using monolithic refractories, and press-fitting/pouring repair methods. However, all of these methods have the following drawbacks. That is, in the spray repair method, existing bricks often crack and fall off due to the moisture contained in the spray material, and there are also problems such as complexity in equipment and environmental pollution. The method of repairing monolithic refractories by pounding them has low work efficiency and is difficult to mechanize, so it has the disadvantage of requiring manual labor at high temperatures. Furthermore, the press-fitting/pouring method requires 3 to 8 hours for repair, which poses a problem in that the operating rate of the equipment is significantly reduced. SUMMARY OF THE INVENTION An object of the present invention is to provide a hot repair method for a degassing immersion pipe for molten steel that solves the problems of the prior art described above and can be performed in a short time with simple work and equipment. The gist of the present invention is as follows. That is, in a method for hot repair of a molten steel degassing immersion tube in which a immersion tube is immersed in molten steel in a ladle and the molten steel is drawn up into a degassing tank and refined, the molten steel is suspended in the steel contained in the ladle prior to the refining. Injecting basic refractory powder particles into the slag in the vicinity of where the dipping tube is immersed to melt the slag or bring it into a semi-molten state;
A molten steel degassing immersion tube comprising the step of immersing the immersion tube in the molten or semi-molten slag and raising and lowering it several times to coat the inner and outer surfaces of the immersion tube with slag. This is a hot repair method. The method of the present invention is an epoch-making method that is completely different in concept and method from conventional methods, and is a repair method using slag coating based on a preventive maintenance concept. The degree to which slag corrodes refractories such as immersion pipes, that is, the activity of slag, is determined by temperature, viscosity at a certain temperature, surface tension, activation energy, ionization or ionic reactivity, and the like.
The present inventors have discovered that by controlling the activity of the slag, the amount of corrosion of the refractory can be reduced, and the immersion pipe can be protected by the slag adhesive layer. That is, before the start of degassing refining of the ladle 2 containing molten steel 4, basic refractory powder 12 is introduced into the vicinity of the immersion tube 6 of the floating slag 10 to lower the temperature of the slag 10. The viscosity is significantly increased to bring the slag 10 into a molten or semi-molten state. Next, the molten or semi-molten slag 1
The dipping tube 6 is immersed in the slag 10, and the ladle 2 is raised and lowered several times, thereby coating the inner and outer surfaces of the dipping tube 6 with the highly viscous slag 10. As the material for the basic refractory powder to be introduced, natural magnesia or brick scraps such as magnesia and magnesia-chromium are preferable because they have a high dissolution rate in the slag and are low cost. Also, the size of the basic refractory powder particles to be added is 30
If it is less than mm, it reacts quickly with the slag and can be operated without any time loss from charging to coating. After adding the basic refractory and coating the immersion tube according to the present invention, the molten steel is sucked up into a degassing tank and refined as usual, but there are no particular changes or problems with respect to the temperature drop of the molten steel, and there are no problems with degassing. Gas refining can be performed. Furthermore, the coating of the dip tube according to the present invention does not need to be carried out for each heat, but can be carried out at the appropriate time by taking into consideration the damaged condition of the dip tube and the properties of the slag. can be significantly improved. EXAMPLE Using natural magnesia and magnesia-chromium brick scrap having the chemical composition and particle size shown in Table 1, hot repair of a dip tube was carried out by the method of the present invention prior to vacuum degassing treatment. In other words, natural magnesia is heated once every 10 heats, and 100 times per heat.
Kg was introduced and the ladle was raised and lowered 5 times to immerse the dipping tube, and then degassing was performed as usual. Further, magnesia-chromium brick waste was charged at a rate of 75 kg once every 5 heats, and the ladle was raised and lowered 5 times in the same manner to coat the dipping tube.

[Table] Table 2 compares the immersion tube life, immersion tube erosion rate, and cost index when the cost of the conventional example is set as 100 for the above-mentioned embodiment of the present invention and the conventional example using the tapping repair method. Indicated. In Table 2, the life of the immersion tube in the example of the present invention is more than twice that of the conventional example, the erosion rate is less than 1/4, and the cost index is significantly reduced to 45 and 58 compared to 100 of the conventional example. ing. Of course, the basic refractory addition and degassing refining after coating are different from normal times.

【table】

[Table] There was no difference. As is clear from the above embodiments, the present invention provides basic refractory powder particles to the slag in a ladle and coats the immersion tube with the slag.
Hot repair of immersion pipes can be carried out at low cost with simple work without the need for special equipment.

[Brief explanation of the drawing]

The accompanying drawing is a schematic partial sectional view of a vacuum degassing apparatus for explaining the method of the present invention. 2... Ladle, 4... Molten steel, 6... Immersion tube, 8...
...Degassing tank, 10...Slag, 12...Basic refractory powder.

Claims (1)

[Claims] 1. In a method for hot repair of a molten steel degassing immersion pipe in which a immersion pipe is immersed in molten steel in a ladle and the molten steel is sucked up into a degassing tank and refined, slag floating in the molten steel in the ladle prior to said refining. A step of injecting basic refractory powder into the vicinity of the immersion tube to melt the slag or semi-molten slag, and immersing the immersion tube in the molten or semi-molten slag and raising and lowering it several times. 1. A hot repair method for a molten steel degassing immersion tube, comprising the steps of: slag coating the inner and outer surfaces of the immersion tube.