JP6988361B2 - RH type vacuum degassing device - Google Patents

Description

The present invention relates to an RH type vacuum degassing apparatus having a high cleaning ability for removing inclusions suspended in molten steel.

Since non-metal inclusions in steel materials deteriorate the performance of steel materials, it is necessary to remove a large amount of non-metal inclusions by refining the molten steel in order to produce steel with high cleanliness. In particular, in the final step of the refining process, the RH type vacuum degassing treatment device is widely and generally used, and the steel material can be upgraded by increasing the cleaning capacity of the RH type vacuum degassing treatment device.

In the RH vacuum degassing treatment, the non-metal inclusions suspended in the molten steel are agglomerated and coalesced, and then the non-metal inclusions that have been agglomerated and coalesced are levitated to the ladle slag to remove the non-metal inclusions from the molten steel. do. It is known that a method of increasing the stirring power density or the ring flow rate of the molten steel is effective for aggregating and coalescing the non-metal inclusions and floating them on the ladle slag for removal.

Patent Document 1 proposes a method of increasing the ring flow rate to the range of 150 to 200 t / min, and Patent Document 2 increases the ring flow rate to 1 to 1.4 times that of the ascending tube in order to increase the ring flow rate. A method to increase it has been proposed. Further, Patent Document 3 proposes a method of increasing the stirring power density during the RH type vacuum degassing treatment to 6 WH / t or more.

On the other hand, if the ring flow rate increases too much, the bare metal adhering to the vacuum chamber may melt into the molten steel as a pollution source, and non-metal inclusions may be generated in the molten steel. Therefore, Patent Document 4 proposes a method of increasing the ring flow rate in the first half of the RH type vacuum degassing treatment to 180 to 210 t / min and reducing the ring flow rate in the latter half to 110 to 140 t / min.

Japanese Unexamined Patent Publication No. 2010-189691 Japanese Unexamined Patent Publication No. 2009-2053539 Japanese Unexamined Patent Publication No. 10-219335 Japanese Unexamined Patent Publication No. 2008-303406

In the conventional technique, in order to remove non-metal inclusions, a method of changing the ring flow rate between the first half and the second half of the treatment has been performed. On the other hand, depending on the conditions, there are problems that the inclusion removal speed is naturally limited and the processing time becomes long.

In view of the above-mentioned problems, it is an object of the present invention to provide an RH type vacuum degassing apparatus capable of efficiently removing non-metal inclusions from molten steel.

The present inventors have studied an RH type vacuum degassing treatment apparatus capable of further increasing the inclusion removal rate even if the ring flow rate is the same. That is, the non-metal inclusions are removed by floating on the surface of the ladle, but when the flow velocity of the molten steel is high, the non-metal inclusions are attracted to the flow of the molten steel passing through the opening of the immersion tube before the non-metal inclusions float. It will be carried to the bottom of the ladle or into the vacuum chamber again. However, when the flow rate of the molten steel is reduced in the vicinity of the opening by reducing the ring flow rate, the stirring in the ladle becomes insufficient, and the floating removal speed of the non-metal inclusions on the ladle surface decreases. Therefore, it is necessary to reduce the flow velocity of the molten steel in the vicinity of the opening without reducing the ring flow rate.

Therefore, as a method of reducing the flow velocity of molten steel in the vicinity of the opening without reducing the ring flow rate, the present inventors have widened the opening at the lower end of the immersion pipe with respect to the upper portion to expand the cross-sectional area. I found. Since the ring flow rate is determined by the inner diameter of the narrowest part of the ascending or descending flow path through the immersion tube, for example, even if only the opening at the lower end of the immersion tube is widened, the ring flow rate is widened. It does not change. Therefore, the non-metal inclusions are more likely to float on the surface of the ladle without being sucked by the flow of the molten steel, and the non-metal inclusions can be efficiently removed from the molten steel.

The present invention has been made as a result of such studies, and the gist thereof is as follows.
(1) RH type vacuum degassing treatment device that performs degassing treatment of molten steel by circulating molten steel through the flow path between the cylindrically shaped immersion pipe of the ascending flow and the cylindrical immersion pipe of the descending flow. And,
A straight portion and a tapered portion are provided in both the ascending flow and the descending flow immersion pipes, so that the cross-sectional area of the opening on the bottom surface of the tapered portion is larger than the cross-sectional area of the straight portion.
The RH type is characterized in that the cross-sectional area of the opening on the bottom surface of the tapered portion is 1.1 to 2.8 times the minimum cross-sectional area of the flow path of the ascending or descending flow through the dipping pipe. Vacuum degassing equipment.
(2) The RH type vacuum degassing treatment apparatus according to (1) above, wherein the cross-sectional area of the opening is the maximum cross-sectional area in the flow path of the ascending flow or the descending flow.

According to the present invention, the cleaning ability can be enhanced without lowering the ring flow rate. As a result, the processing time required for cleaning can be shortened, the amount of recirculated gas can be reduced, and the processing cost can be reduced.

It is a figure for demonstrating the outline of the RH type vacuum degassing processing apparatus. It is a figure which shows an example of the immersion tube which has a taper. It is a figure which shows the relationship between the ratio K / K ₀ and the ratio A _a / A _t.

Hereinafter, the RH type vacuum degassing treatment apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 shows an example of an RH type vacuum degassing treatment apparatus, FIG. 1A shows an example of an RH type vacuum degassing treatment apparatus according to the present embodiment, and FIG. 1B shows a conventional example. An example of the RH type vacuum degassing treatment apparatus is shown.
As shown in FIG. 1, the configuration of the RH type vacuum degassing treatment device excluding the immersion tube may be a widely generally used configuration. Hereinafter, the specific structure of the immersion tube 2 shown in FIG. 1A will be described.

The immersion tube 2 has a cylindrical shape, and the refractory thickness of the immersion tube 2 is preferably 200 to 350 mm. If the thickness of the refractory material of the immersion tube 2 is smaller than 200 mm, the thermal effect on the core metal for maintaining the shape provided inside the immersion tube becomes large, and the immersion tube 2 may be deformed due to temperature changes before and after the treatment. There is. On the other hand, if it is larger than 350 mm, the cost of the refractory material increases and the inner diameter may become smaller because the immersion tube needs to be housed in the ladle.

It is desirable that the position of the recirculation gas blowing tuyere 3 provided in the immersion pipe 2 on the ascending flow side is at a height of 150 to 600 mm from the bottom surface of the lower end portion 4 of the immersion pipe. At a position lower than 150 mm from the bottom surface, the pipe connected to the tuyere may be deformed due to the large heat effect from the bottom surface. Further, at a position higher than 600 mm from the bottom surface, the distance between the tuyere for blowing the recirculated gas and the surface of the molten metal becomes short, and the degassing treatment may be insufficient due to the bubbles of the recirculated gas.

FIG. 2 is an enlarged view of the immersion tube 2. In the present embodiment, the dipping tube 2 is provided with a tapered portion 5. The tapered portion 5 provided in the dipping tube 2 may be provided at any position of the dipping tube 2, but it is necessary to make the cross-sectional area of the opening 7 on the bottom surface larger than the cross-sectional area of the straight portion 6. It is desirable that the cross-sectional area of the opening 7 on the bottom surface is the largest. Further, the length of the tapered portion 5 is preferably 100 mm or more. This is because if it is less than 100 mm, the pressure loss in the immersion tube becomes large and the ring flow rate may decrease. Comparing FIGS. 1 (a) and 1 (b), by providing the tapered portion 5 in this way, the non-metal inclusions 8 are more likely to float on the surface of the ladle without being sucked by the flow of molten steel. Therefore, the non-metal inclusions 8 can be efficiently removed from the molten steel.

Further, in the example shown in FIG. 1A, the cross-sectional area of the flow path in the straight portion 6 is the minimum, and the cross-sectional area in the opening 7 is larger than that, but the cross-sectional area is not limited to such a shape. It is sufficient that the cross-sectional area of the opening 7 is not minimized in the ascending or descending flow path. That is, since the ring flow rate is determined by the minimum cross-sectional area in the ascending or descending flow path through the immersion pipe, if the cross-sectional area of the opening 7 is larger than that, the molten steel in the vicinity of the opening The flow velocity can be reduced. That is, it is not always necessary to provide a range in which the cross-sectional area of the flow path is the minimum and constant as in the straight portion.

Next, in order to confirm how much the cross-sectional area of the opening 7 on the bottom surface should be increased to obtain a more effective effect, the RH in which the opening 7 at the lower end of the dipping tube 2 as shown in FIG. 1A is widened. The influence on the cleanliness when the type vacuum degassing treatment apparatus 1 was used was investigated using 300 tons of molten steel. The survey method is as follows.

The C concentration contained in the ladle 9 was 0.04 to 0.3% by mass, the Si concentration was 0.05 to 0.4% by mass, the Mn concentration was 0.5 to 1.8% by mass, and the Al concentration was 0. 01-0.08% by mass, T.I. The dipping tube 2 attached to the vacuum chamber 11 was immersed in 300 tons of molten steel 10 having an O concentration of 0.0040 to 0.0045% by mass and a total alloy component and impurity component of 2% by mass or less. While evacuating the inside of the vacuum chamber 11 from 67 to 1330 Pa, a total of 1.5 to 2.0 Nm ³ / min of recirculated gas was introduced from the recirculated gas blowing tuyere 3 provided on the inner surface of one of the immersion pipes 2, and the molten steel 10 was introduced. Started to recirculate. After 18 to 20 minutes of recirculation, the RH vacuum degassing treatment was completed. Before and after the treatment, T.I. The change in O concentration was measured.

Here, the immersion tube 2 provided in the RH type vacuum degassing device 1 shown in FIG. 1A has a cylindrical shape, the inner diameter of the straight portion 6 is 650 mm or 750 mm, and the refractory thickness is 280 mm. And said. Further, a taper was provided in a range from the bottom surface to a height of 150 to 200 mm, and the thickness of the refractory material at the lower end portion 4 of the immersion tube 2 was set to 80 to 280 mm. The example in which the refractory thickness of the lower end portion 4 is 280 mm is a condition in which no taper is provided for comparison. The recirculation gas blowing tuyere 3 was provided at a height of 300 to 400 mm from the bottom surface. Then, T.I. O concentration and T.I. after treatment. The O concentration was measured.

Here, as an index of the size of the taper, the evaluation is performed using the ratio A _a / A _{t of the cross-sectional area (A a ) of the opening 7 and the cross-sectional area (A t} ) of the flow path in the straight portion 6. rice field. Here, when the taper is provided, the T.I. O concentration and T.I. after treatment. The rate of change from the O concentration (TO concentration after treatment / TO concentration before treatment) is defined as K, and T.I. O concentration and T.I. after treatment. The rate of change from the O concentration (TO concentration after treatment / TO concentration before treatment) is defined _{as K 0.} 3 shows, the ratio K / K ₀ of the rate of change K and the change rate K _0, showing the relationship between the ratio _{A a} / A _t.

As shown in FIG. 3, the ratio K / K ₀ became smaller _{as the ratio A a} / A _{t became larger than 1.} The smaller the ratio K / K _{0, the more T.I.} Since the O concentration is low, the cleaning ability of the molten steel being processed is improved as the _{ratio A a} / A _{t is larger than 1.} In particular, the ratio _{A a} / A _t is the effect became prominent at 1.1 or more. It is considered that this is because the flow velocity of the molten steel passing through the opening of the dipping tube decreased, and the ratio of the oxide-based inclusions suspended around the opening decreased to be sucked into the molten steel flow.

However, although not shown, when the ratio A _a / A _t exceeds 2.8, the ratio K / K ₀ becomes an almost constant value, and the effect is saturated. In addition, if the cross-sectional area of the opening is excessively expanded, the flow velocity of the molten steel near the opening will decrease, which will have the effect of suppressing the suction of non-metal inclusions, and the area affected by the opening will increase, resulting in suction. It is considered that the effect of increasing the amount of non-metal inclusions is balanced.

From the above test results, the cross-sectional area of the opening is 1.1 of the minimum cross-sectional area of the ascending or descending flow path through the immersion pipe (in the case of the test, the cross-sectional area of the flow path in the straight portion). It is desirable that it is ~ 2.8 times.

Next, an example of the present invention will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is based on this one condition example. Not limited. The present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

In this embodiment, as shown in FIG. 1 (a), the molten steel was cleaned by using an RH type vacuum degassing device having a tapered dipping tube. For comparison, as shown in FIG. 1 (b), a cleaning treatment of molten steel was also performed using an RH type vacuum degassing treatment device having no taper on the immersion pipe. In each case, the immersion tube used was a cylindrical shape.

First, the C concentration is 0.04 to 0.3% by mass, the Si concentration is 0.05 to 0.4% by mass, the Mn concentration is 0.5 to 1.8% by mass, and the Al concentration is 0.01 to 0. 08% by weight, T.I. After 300 tons of molten steel having an O concentration of 0.0040 to 0.0045% by mass and a total alloy component and impurity component of 2% by mass or less is housed in a ladle and the immersion tube is immersed in the molten steel. The inside of the vacuum chamber was depressurized to 133 to 1100 Pa, and Ar gas was blown at 1800 to 2000 NL / min from the recirculation gas tuyere installed in the ascending pipe to start the recirculation. The recirculation time was 20 minutes. In the test, the test conditions and test results in which the inner diameters of the straight portion of the immersion tube are 550 mm, 650 mm, and 750 mm, respectively, are shown in Table 1, Table 2, and Table 3, respectively.

Test No. of the example of the present invention. 2 to 5, 7 to 10, 12 to 15 are the test Nos. Of Comparative Examples having no taper. _{The ratio K / K 0} was smaller than that of 1, 6 and 11. That is, T.I. It was confirmed that the O concentration became smaller and the non-metal inclusions were more removed from the molten steel. As described above, by using the RH type vacuum degassing treatment apparatus having the shape of the immersion tube specified by the present invention, the cleaning speed during the treatment is increased, and the T.I. It was confirmed that the O concentration could be lowered.

1 RH type vacuum degassing treatment device 2 Immersion pipe 3 Tub 4 Lower end 5 Tapered part 6 Straight part 7 Opening 8 Non-metal inclusions 9 Ladle 10 Ladle 11 Vacuum tank

Claims (2)

An RH type vacuum degassing device that recirculates molten steel through a flow path between an ascending cylindrical dipping tube and a descending cylindrical dipping tube to degas the molten steel. ,
A straight portion and a tapered portion are provided in both the ascending flow and the descending flow immersion pipes, so that the cross-sectional area of the opening on the bottom surface of the tapered portion is larger than the cross-sectional area of the straight portion.
The RH type is characterized in that the cross-sectional area of the opening on the bottom surface of the tapered portion is 1.1 to 2.8 times the minimum cross-sectional area of the flow path of the ascending or descending flow through the dipping pipe. Vacuum degassing equipment. The RH type vacuum degassing treatment apparatus according to claim 1, wherein the cross-sectional area of the opening is the maximum cross-sectional area in the flow path of the ascending flow or the descending flow.

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