JPH0452209A - Immersion tube for degassing refining - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a degassing refining immersion tube for degassing while circulating molten steel between an RH degassing tank and a molten steel ladle.

[Conventional technology] Recently, as steel materials have become more sophisticated, special steels with the content of various elements adjusted to extremely small amounts, such as ultra-low nitrogen steel and ultra-low Demand for carbon steel is increasing, and there is a need for technology to quickly and stably melt them. Against this background, RH degassing refining is attracting attention as a technology for efficiently denitrifying and decarburizing molten steel.

A conventional RH degassing tank has a pair of pipes attached to its lower tank, and these pair of pipes are immersed in molten steel to suck up the molten steel into the tank under reduced pressure, and one submerged pipe is filled with inert gas. By blowing the molten steel, the molten steel is circulated between the degassing tank and the molten steel ladle and degassed.

[Problem to be solved by the invention] In order to improve the reaction rate of RH degassing refining, it is necessary to increase the molten steel recirculation flow rate, and various techniques have been studied to increase the recirculation flow rate. has been done. In order to increase the flow rate of molten steel, it is necessary to increase the amount of inert gas blown or to increase the molten steel flow cross-sectional area of the immersion pipe. However, since there is a technical limit to increasing the amount of gas blown, expanding the molten steel flow cross-sectional area of the immersion tube is being considered as a technique for increasing the recirculation amount.

For example, according to the invention described in Japanese Unexamined Patent Publication No. 59-85815, the cross-sectional shape of a pair of immersion tubes is each an ellipse, and the immersion tubes are arranged so that the short axis of the ellipse faces the center of the degassing tank. The cross-sectional area of the molten steel is expanded by avoiding mutual interference between the two.

However, in the above-mentioned immersion pipe, since the pair of immersion pipes (rising pipe and downcomer pipe) and the lower degassing tank are each flange-connected, both flanged joints may interfere with each other, and the degassing tank body may There is a limit to increasing the molten steel flow cross-sectional area of the immersion pipe when the diameter of the pipe is kept constant. In other words, the above-mentioned elliptical flow path immersion tube also eliminates the conventional type (
The limit is about twice the recirculation flow rate of a dipping tube (each having a perfect circular cross-sectional shape), and this is insufficient for stable and rapid degassing of ultra-low nitrogen steel and the like.

The present invention has been made in view of the above circumstances, and aims to provide a degassing refining immersion pipe that can increase the flow rate of molten metal, has excellent strength and durability, and is inexpensive. purpose.

[Means for Solving the Problems] The inventors have conducted various studies on the shape of the immersion tube in order to increase the flow rate of molten steel and improve the degassing ability. As a result, as disclosed in Japanese Patent Application No. 1-20210, it was decided to integrate the ascending pipe and the downcomer pipe and partition them using a partition to enlarge the flow cross-sectional area of molten steel.

The immersion pipe for degassing refining according to the present invention has a rising part that is immersed in molten metal and sucks up the molten metal into the degassing tank main body, and a descending part that returns the molten metal sucked up to the degassing tank main body, It is characterized in that the lower part and the descending part are integrally formed, and the cross section of the molten metal flow path of both is formed in an elliptical or approximately elliptical shape.

In this case, the cross section of the molten metal flow path should be set at a long axis/short axis ratio of 2
It is preferable to form an ellipse as described above, and it is more preferable to form an ellipse with a major axis/minor axis ratio of 2.5 to 3. A larger major axis/minor axis ratio of the ellipse is advantageous for increasing the flow cross-sectional area, but from the viewpoint of stability of the lining brick, the longer axis/minor axis ratio is better.
It is more advantageous to reduce the minor axis ratio to give the curved shape.

[Function] In the degassing refining immersion pipe according to the present invention, the problem of mutual interference between the joint flanges is solved by integrating the ascending section and the descending section, so that the molten metal flow paths of both can be expanded respectively. It becomes possible to do something. Therefore, it is possible to expand the molten metal flow cross-sectional area and increase the molten metal circulation flow rate.

Further, since the molten metal passage is formed so that the cross-sectional shape is elliptical or approximately elliptical, it is difficult to remove the lining brick. This is because when the lining bricks are piled up linearly, the competition between the bricks becomes weaker, and the self-fixing power of the bricks decreases.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a longitudinal cross-sectional view schematically showing a lower tank of a degassing refining apparatus according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of an integrated immersion tube. Rails are laid on the first floor of the building of the RH degassing facility, and a ladle (not shown) is transported from the converter factory by a traveling truck. A degassing tank 10 is provided in the upper part of the building, and a lifting table (not shown) for raising and lowering the ladle is installed directly below this tank.

The degassing tank 10 has an exhaust passage (not shown) in the upper tank 11.
is formed, and the gas inside the tank is exhausted. This upper tank 11 has a lower tank 20 with a flange 12.22.
are removably connected. The inner diameter of the iron shell of the upper tank 11 is approximately 3 m.

The lower tank 20 has a main body 21 and a dip tube 24, both of which are removably connected by a flange 23.25. A soft packing (not shown) is inserted between the refractory lining of the main body portion 21 and the refractory lining of the immersion tube 24.

This packing is made of, for example, a flexible magnesia monolithic refractory.

The upper half of the dip tube 24 is covered with an iron shell 2, and the lower half is covered with a castable tube 30.

A pair of molten metal passages 32 are formed in the immersion pipe 24, and each molten metal passage 32 is surrounded by a lining brick 27. The top layer of the dipping tube 24 is covered with paving bricks 28°40. Between the lining bricks 27 of the pair of molten metal flow paths 32, from the top, lay bricks 401 and judgment bricks 41.
．． Castable 42, water cooling box 44. Firebrick 4
5. A castable 46 is provided. A cylindrical core material 26 is embedded in the lower half of the dip tube 30, and a castable material 30 is sprayed onto the outer periphery of the core material 26.

In addition, four wedges 43 are used to prevent the bricks from protruding.
is placed over the center paving brick (work brick) 40 and the judgment brick (permanent brick) 41. The wedge 43 is thick at the upper part and thin at the lower part, and is driven so that the upper part of the wedge 43 is not exposed on the upper surface of the paving brick 40.

A gas pipe (not shown) passes through the refractory and opens at one molten metal passage 32. This gas line is connected to an argon gas supply.

As shown in FIG. 2, each of the molten metal passages 32 has an elliptical cross-sectional shape, and is arranged so that the short axes of both ellipses are aligned in a straight line passing through the central axis of the degassing tank 20. There is.

Next, a case where molten steel is degassed using the above degassing refining immersion pipe will be described.

A ladle of converter molten steel with a carbon concentration [C] or approximately 300 ppc
(not shown) and transported to a degassing treatment facility. The amount of molten steel is approximately 250 tons, which is covered by a small amount of slag. The ladle is lifted, the immersion tube 24 is immersed in the ladle-like molten steel, and the inside of the degassing tank 10 is depressurized to a predetermined pressure. As a result, molten steel is sucked up into the degassing tank 10.

A limit switch provided on the lifting table lifting device is turned on and a signal is sent to the process computer. When a signal is input to the computer, a command signal is sent to the inert gas supply source based on the signal, and a predetermined flow rate of inert gas is supplied to the gas blowing pipe 21.

400 ON per minute to one molten metal flow path 32 via a gas pipe
Blow inert gas at a flow rate of 1). As a result, the apparent specific gravity of the molten steel decreases, and the molten steel flows into the flow path 3 along with gas bubbles.
Rise within 2. The hot water level in the degassing tank rises, splash occurs, and the [C] in the molten steel is gasified, which is then exhausted. Molten steel flows from one flow path 32 to the other flow path 3.
2 and circulate between the ladle and the degassing tank 10. A predetermined amount of a predetermined alloy material is added to adjust the composition of molten steel. Decarburization of molten steel progresses, and the amount of [C] becomes approximately 15 ppm.
Stop blowing inert gas when the temperature drops to .

Next, the effects of the above embodiment will be explained with reference to FIGS. 3 and 4.

Figure 3 is a graph showing the results of a comparison between the immersion tube of the above embodiment and the conventional immersion tube regarding the relationship between the argon gas injection amount on the horizontal axis and the molten steel circulation flow rate on the vertical axis. It is. In the figure, curve A shows the results using the dip tube of the above example, and curve B shows the results using the conventional dip tube. As is clear from the figure, when the amount of argon gas blown is the same as 4, the molten steel circulation flow rate increases significantly in the above embodiment compared to the conventional example.

FIG. 4 is a graph showing the results of an investigation into the relationship between the degassing time on the horizontal axis and the carbon content [C] of molten steel on the vertical axis. In the figure, the curve C shows the results of the conventional method, and the curve shows the results of the example in which the molten steel circulation flow rate was 300 tons per minute. As is clear from the figure, when the immersion tube of the above example is used and the molten steel circulation flow rate is 300 tons per minute, [C] can be reduced to 10 ppm or less in a short time, and the molten steel can be reduced to an extremely low level. It was possible to quickly decarburize to the level of carbon steel.

[Effects of the Invention] According to the present invention, the molten steel flow cross-sectional area of the immersion pipe is expanded, and the molten steel circulation flow rate can be significantly increased compared to the conventional method. For example, a conventional separate perfect circular dip tube has a maximum of 25
Although we were only able to obtain a molten steel flow cross-sectional area of up to 50cm2,
In the integrated elliptical immersion tube of the present invention, the molten steel flow cross-sectional area of the ascending part and the descending part reaches approximately 14169 cm2 in total, which is approximately 5.6 times larger than that of the conventional type.

As a result of the second, the decarburization speed of degassing refining is dramatically increased, and ultra-low carbon steel with a carbon content of several ppm to several tens of ppmI11 can be rapidly and stably produced.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view schematically showing a lower tank of an RH degassing tank apparatus in which a degassing refining dip tube according to an embodiment of the present invention is used, and FIG. 2 is a cross-sectional view of the integrated dip tube. , FIG. 3, and FIG. 4 are graphs for explaining the effects of the embodiments of the present invention, respectively. 10... Degassing tank, 12 22, 23.25... Flange, 20... Lower tank, 24... Immersion pipe, 27° 28.40, 41.45... Brick, 30, 42゜4
6... Castable, 32... Molten metal flow path, Applicant's representative Patent attorney Takehiko Suzue Diagram

Claims (1)

[Claims] It has a rising part that is immersed in the molten metal and sucks up the molten metal into the degassing tank main body, and a descending part that returns the molten metal sucked up to the degassing tank main body. A immersion tube for degassing refining, characterized in that the cross section of the molten metal flow path is formed in an elliptical or approximately elliptical shape.