JPH02247324A - Immersed pipe for degasification refining - Google Patents

Abstract

PURPOSE:To increase the amt. of molten steel to be circulated and to agitate the molten steel in a ladle to accelerate the degasification rate by integrating the ascending part and descending part for molten steel through a partition and reducing the cross-sectional area of the molten steel discharge port of the descending part. CONSTITUTION:The immersed pipe 20 for degasification refining is formed by the ascending part 30, the descending part 32 integrated with the ascending part and the partition 26. A gas is blown into the ascending part 30 by a gas blowing means 21, and molten steel 3 is sucked up into a degasification bath main body 11. The sucked up molten steel 3 is returned through the descending part 32. The partition 26 is formed so that the cross-sectional area of the molten steel discharge port of the descending part 32 is made smaller than that of the molten steel passage of the descending part 32 at the same level with the gas blowing position.

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.

[Prior Art] Recently, there has been an increase in demand for ultra-low carbon steel with an extremely small amount of carbon content, and there is a need for a technology for quickly and stably melting this steel. Against this background, RH degassing refining is attracting attention as a technology for efficiently decarburizing molten steel.

For this reason, in order to improve the decarburization rate in RH degassing refining, increasing the recirculation flow rate of treated molten steel has been studied.

A conventional RH degassing tank has a pair of removable pipes at the bottom of the tank, and the pair of pipes are immersed in molten steel to suck up the molten steel into the tank main body under reduced pressure. The molten steel is degassed while being circulated between the degassing tank and the molten steel ladle by blowing inert gas into the molten steel. Therefore, in order to increase the recirculation flow rate of treated molten steel, it is necessary to increase the amount of gas blown or to increase the molten steel flow cross-sectional area of the immersion pipe. However, there is a technical limit to increasing the amount of gas blown. As a result, various studies have been made to expand the molten steel flow cross-sectional area of the immersion pipe as a direction for conventional techniques for increasing the molten steel circulation flow rate.

[Problems to be Solved by the Invention] However, in the conventional RH degassing tank, the immersion pipes (rising pipe and downcomer pipe) and the degassing tank body are each connected by flanges, and the flanges of the rising pipe and the downcomer pipe If the joints interfere with each other and the diameter of the degassing tank body is constant, there is a limit to increasing the molten steel flow cross-sectional area of the immersion pipe.

As a technique for increasing the flow rate of molten steel, JP-A-59
There is an invention described in JP-A-85815. According to this, the cross-sectional shape of a pair of immersion tubes is each an ellipse, and the short axis of the ellipse is oriented toward the center of the degassing tank to avoid interference between the immersion tubes and to expand the molten steel flow cross-sectional area. There is.

However, the above-mentioned immersion tube is inferior in strength and durability and has a short lifespan compared to a perfectly round one.

Further, since the above-mentioned dip tube has a special shape, manufacturing cost and maintenance cost are high, and manufacturing thereof is generally difficult.

Incidentally, the degassing reaction is affected not only by the stirring state of the molten steel in the degassing tank but also by the stirring state of the molten steel in the pot. This is because the agitation force of the downcomer discharge flow is weak.
This is because it takes a long time for the molten steel in the pot to be mixed uniformly. Therefore, in order to promote the degassing reaction, it is necessary to increase the flow rate of the molten steel discharged into the ladle from the downcomer pipe, improve the stirring of the molten steel in the ladle, and shorten the uniform mixing time.

The present invention has been made in view of the above circumstances, and provides a degassing refining immersion tube that can increase the flow rate of molten steel circulating and shorten the time for uniformly mixing molten steel in a ladle. The purpose is to

[Means for Solving the Problems] The degassing refining immersion pipe according to the present invention includes a rising part for blowing gas by a gas blowing means and sucking up molten metal into the degassing tank body, and integrally formed with the rising part. and a descending part for discharging the molten metal sucked into the degassing tank main body, and a partition separating the rising part and the descending part, and the molten metal flow cross-sectional area of the molten metal discharge port of the descending part is larger than that of the rising part. The partition is characterized in that the partition is formed so as to be smaller than the molten metal flow cross-sectional area of the descending part at the same level as the gas injection position of the part.

[Function 1] In the degassing refining immersion pipe according to the present invention, the rising part and the descending part are integrally formed, and a partition is provided between them, so that the rising part and the descending part can be connected to each other through the partition. Since they are adjacent to each other, it is possible to increase the diameter of both. Therefore, the effective cross-sectional area for the flow of the molten metal in the ascending section and the descending section is expanded, and the amount of molten metal recirculated is increased.

In addition, the molten metal flow cross-sectional area of the molten metal discharge port in the descending section is
Since the partition is formed so that the molten metal flow cross-sectional area of the descending section is smaller than the molten metal flow cross-sectional area of the descending section at the same level as the gas injection position of the ascending section, the molten metal flows from the discharge port of the descending section with almost no reduction in the recirculation amount. The discharge flow rate increases. As a result, the molten metal in the pot is strongly stirred by the discharged molten metal flow, the time for uniform mixing of the molten metal in the pot is shortened, the degassing reaction is promoted, and the stirring power of the molten metal is increased, so the deoxidation reaction is also carried out. Promotion (
inclusions removed).

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

As shown in FIG. 2, the degassing tank 10 is located above the ladle 2, and the immersion pipe 20 at the bottom of the degassing tank is immersed in the molten steel 3 in the ladle. The ladle 2 is mounted on a truck, and is raised and lowered together with the truck by a lifting device (not shown). Note that the molten steel 3 in the ladle is covered with molten slag 4. The degassing tank 10 is fixed to a building and has an exhaust port 12 at the top. This exhaust port 12 is communicated with an exhaust gas device (not shown) to degas I! The gas inside 10 is exhausted. The main body 11 of the degassing tank consists of an upper main body 11a and a lower main body 11b, both of which are detachably connected by a flange joint 13. Further, the upper part of the degassing tank main body 11 and the immersion pipe 20 is covered with an iron skin 15.

FIG. 1 is an enlarged vertical sectional view of the lower part of a degassing tank having a degassing refining immersion pipe according to a first embodiment of the present invention. The dip tube 20 has an outer peripheral portion 22 and a partition 26 that partitions the interior into an ascending section 30 and a descending section 32. Rising part 30
A gas blowing pipe 21 is connected to the molten steel flow path, and an inert gas is blown thereinto. The partition 26 has a constricted portion 29 having a chevron-shaped cross section at its lower portion, and the molten steel discharge port of the descending portion 32 is narrowed by this constricted portion 29 .

FIG. 3 is a cross-sectional view of the dip tube 20. In the outer peripheral part 22 of the dip tube 20, a fireproof brick 28 is pasted inside a cylindrical core material 24, and a castable brick 23 is pasted on the outside of the core material 24.
is provided to a predetermined thickness. Further, in the partition 26, firebricks 28 are pasted on both sides of the core material 27. In this case, iron plates with a thickness of several millimeters to 10-odd millimeters are used for the core materials 24 and 27, chromium-magnesia bricks with excellent spalling resistance are used for the refractory bricks 25 and 28, and high alumina castables are used for the castables 23. It is preferable. An example of the size of each part of the immersion tube 20 is shown below.

Thickness of the upper part of the partition 26 T; 50es Radius R of the molten steel passage at the gas injection position of the rising part 30; 95 cs Width W of the molten steel passage at the molten steel discharge port of the descending part 32; The thickness T is set at 30 to 80 cm in order to suppress the decrease in the molten steel flow cross-sectional area while considering corrosion resistance during continuous use.
It is desirable that the range be within the range of .

Moreover, the width W is defined as 100% of the molten steel flow cross-sectional area at the gas injection position of the rising part 30, whereas the molten steel flow cross-sectional area at the molten steel discharge port of the descending part 32 is 30% to 100%.
It is preferable to narrow down the range to 70%, and
It is most preferable to narrow it down to about 0%.

Next, a case will be described in which ultra-low carbon steel is melted using the above-mentioned degassing tank.

Converter molten steel ladle 2 with carbon concentration [C] of approximately 300 ppm
The steel is then transported to a degassing facility.

The amount of molten steel 3 is approximately 250 tons. Lift ladle 2,
The immersion pipe 20 is immersed in the ladle self-melting steel 3, and the inside of the degassing tank 10 is depressurized to a predetermined pressure. As a result, the molten steel 3 is sucked up into the degassing tank 10. Next, a predetermined flow rate of argon gas, for example, 400 ml per minute, is supplied to the molten steel flow path of the rising section 30 through the gas blowing pipe 21. ONj? Blow in argon gas at a flow rate of . As a result, the apparent specific gravity of the molten steel 3 decreases, and the molten steel 3 rises in the flow path of the rising section 30 together with gas bubbles. The molten metal surface above the rising part 30 rises, splash occurs, and [C] in the molten steel reacts with [01] to produce CO.
gas or CO2 gas, which is exhausted. In this way, decarburization of the molten steel 3 is promoted.

Next, the effects of the embodiment will be explained with reference to FIGS. 4 to 6.

FIG. 4 is a graph showing the results of comparing the present invention and the conventional method with respect to the relationship between the two, with the horizontal axis representing the argon gas injection amount and the vertical axis representing the molten steel circulation flow rate. In the figure, curve A
curve B shows the results of the present invention, and curve B shows the conventional results. As is clear from the figure, when the amount of argon gas blown is the same, the molten steel circulation flow rate is significantly increased in the present invention compared to the conventional method.

FIG. 6 is a graph showing the results of an investigation into the relationship between the two when the horizontal axis is the overhanging length of the lower end of the partition, the vertical axis is the molten steel circulation opening, and the radius R is 95 cm. As is clear from the figure, the overhang length is 50
The molten steel reflux flow rate is almost constant in the range below IllI, but when the length exceeds 50 mm, it gradually decreases, and when the length exceeds 70 m, the molten steel reflux flow rate decreases rapidly.

In Figure 7, the horizontal axis represents the length of the overhang at the bottom of the partition, the vertical axis represents the uniform mixing time of the molten steel in the pot, and the radius R is 95 cm.
It is a graph figure which shows the result of investigating the relationship between both when m is set. As is clear from the figure, when the overhang length is about 50 mm, the uniform mixing time is about 30 seconds, which is the shortest. From the relationship between the above-mentioned reflux flow rate and uniform mixing time, it is optimal to set the molten steel flow cross-sectional area to 50% as described above.

FIG. 5 is a graph showing the results of an investigation into the relationship between the degassing time on the horizontal axis and the carbon content m [C] of molten steel on the vertical axis. In the figure, curve C shows the conventional results when the molten steel circulation flow rate was 150 tons per minute, and the curved line shows the results of the embodiment of the present invention where the molten steel circulation flow rate was 300 tons per minute.

As is clear from the figure, when the molten steel circulation flow rate was 300 tons per minute, [C] could be reduced to 10 ppm or less, and the molten steel could be rapidly decarburized to the region of ultra-low carbon steel.

Next, a second embodiment of the present invention will be described with reference to FIGS. 8 and 9. It should be noted that explanations of parts that this second embodiment has in common with the first embodiment described above will be omitted.

As shown in FIG. 8, the -E portion of the partition 56 of the immersion tube 50 is biased toward the gas blowing tube 21 side, and has an inclined surface as a constriction portion 59 at its lower portion.

The throttle part 59 is inclined toward the opposite side of the gas blowing pipe 21 and is formed so that the molten steel discharge port of the descending part 62 is narrower than the molten steel suction port of the rising part 60. In this case, the molten steel flow cross-sectional area of the discharge port of the descending section 62 is
When the molten steel flow cross-sectional area at the gas injection position is taken as 100%, it is preferably formed so that the cross-sectional area is about 50% of this.

According to the second embodiment, the aperture shape of the partition can be made into a simple structure, and the refractory cost can also be reduced.

[Effect of the Invention 1] 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 pair of conventional dip tubes can handle up to 2550c.
However, in the immersion tube of the present invention, the molten steel flow cross-sectional area of the ascending section and descending section reaches approximately 14,169 cm, which is 5.6 times that of the conventional method. Cross-sectional area is secured. Further, according to the present invention, since the molten metal discharge port of the descending portion is narrowed by the partition, the molten metal discharge flow rate increases and the molten metal in the pot is strongly stirred.

Therefore, the time for uniformly mixing the molten metal in the pot can be significantly shortened. As a result, the decarburization speed of degassing scouring increases dramatically, and the carbon content decreases from several ppm to several tens of ppm.
It is possible to quickly and stably manufacture high-quality ultra-low carbon steel.

In addition, the strong stirring of the molten metal in the pot according to the present invention also improves the deoxidation (inclusion removal) speed, making it possible to significantly shorten the overall processing time.

[Brief explanation of drawings]

FIG. 1 is an enlarged longitudinal sectional view of the lower part of a degassing tank having a degassing refining immersion pipe according to a first embodiment of the present invention, FIG. 2 is a schematic diagram of the degassing tank, and FIG. FIGS. 4 to 7 are graphs for explaining the details of this invention, and FIG. 8 is a cross-sectional view of a submerged tube according to a second embodiment of this invention. FIG. 9 is an enlarged vertical cross-sectional view of the lower part of the degassing tank having the dip tube, and FIG. 9 is a cross-sectional view of the dip tube of the second embodiment. 10.40; Degassing tank, 20.50. Immersion tube, 21; Gas blowing tube, 22; Outer periphery, 26;. 56; Partition, 29, 59. Aperture part, 30゜60; Ascending part, 32,62; Descending part Applicant's representative Patent attorney Takehiko Suzue Tank length σL (mm) (N shadow 4 small) Fig. Fig. Fig. et al. n Fig.

Claims (1)

[Claims] a rising part that blows gas with a gas blowing means and sucks up the molten metal into the degassing tank main body; a descending part that is formed integrally with the rising part and discharges the molten metal sucked up into the degassing tank main body;
a partition separating the ascending section and the descending section, the molten metal flow cross section of the molten metal discharge port of the descending section being at the same level as the gas blowing position of the descending section; A immersion pipe for degassing refining, characterized in that the partition is formed so as to be smaller than the cross-sectional area.