JP2797829B2 - Tundish infusion tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tundish injection tube used for continuous casting. More specifically, the present invention suppresses the secondary oxidation of molten steel while reducing the flow rate of inert gas such as Ar gas ejected from the injection pipe into the molten steel, as well as reducing the flow rate of the metal onto the inner wall surface of the injection pipe. The present invention relates to a tundish injection tube capable of reliably preventing adhesion.

[0002]

2. Description of the Related Art In continuous casting of molten steel, it is necessary to suppress secondary oxidation of the molten steel in each step. For example, as a technique for suppressing the secondary oxidation of molten steel between a ladle and a tundish, FIG. 2 shows a continuous casting apparatus that performs a commonly used injection pipe upper sealing method (injection pipe kinshasa sealing method). Partially omitted and shown conceptually.

In FIG. 1, a ring pipe 23 is provided to blow an inert gas from a ladle (not shown) to an injection flow 22 via an injection pipe 21 so that the injection flow 22 is securely sealed. Inject molten steel into tundish 24. The injected molten steel 28 is supplied to the mold 27 via the sliding nozzle 25 and the immersion nozzle 26 of the tundish 24.

However, in the apparatus shown in FIG.
The splash mainly generated by the collision of the 22 with the molten steel 28 in the tundish 24 causes the base metal to adhere and accumulate on the inner wall surface of the injection pipe 21, so that the molten steel cannot be cast by a normal injection flow. In other words, casting cannot be performed for a long time due to the large size of the deposited metal, which makes it difficult to apply the method to actual continuous casting. Must be sealed with an inert gas, which requires a large amount of inert gas, which is not economical.In addition, the seal with the inert gas is completely broken during continuous casting. ) And the secondary oxidation of the molten steel occurs, and its improvement has been required.

Therefore, Japanese Utility Model Publication No. Sho 60-27580 proposes an injection pipe capable of preventing the adhesion of metal to the inner wall surface. FIG. 3 is an explanatory view schematically showing a configuration of an injection pipe proposed by Japanese Utility Model Publication No. 60-27580. FIG. 3A is an overall explanatory view in which the injection pipe 34 is incorporated, and FIG. 2B is an enlarged explanatory view showing the structure of the outer wall (peripheral wall) of the injection pipe 34.

In FIG. 1A, a sliding nozzle 32 provided at the bottom of a ladle 31 is composed of a sliding upper nozzle 32a, a sliding upper plate 32b, a sliding lower plate 32c, and a sliding lower nozzle 32d from above. Splash 35a scattered from sliding lower nozzle 32d and injection flow 36 impinge on molten steel 35 on the inner wall surface of injection pipe 34, which is disposed above tundish 33 and used by being immersed in molten steel. The metal is likely to adhere due to 35b, but inside the peripheral wall of the injection pipe 34 according to this proposal,
As shown in FIG. 3B, an inert gas supply path 37 is built in and a plurality of inert gas outlets 38 are connected to each other in the axial direction. Is spouted, so that adhesion of the bullion is prevented.

[0007]

[Problems to be Solved by the Invention] However,
The technique proposed in Japanese Patent Publication No. 580 also has the following problems. Since the range of the outlet 38 of the inert gas outlet extends over substantially the entire area of the molten steel flow 36, the molten steel flow 36 may be disturbed.
36 is disturbed. During continuous casting, it takes time to recover the seal breach due to the inert gas, and secondary oxidation of molten steel may occur. Although the amount of metal ingot has been improved from before,
It is still reduced to only about half of the conventional method,
Further improvement is needed.

Here, an object of the present invention is to
To improve the inert gas seal in the injection pipe proposed by Japanese Patent Publication No. 0, and to significantly reduce, preferably desirably completely eliminate the occurrence of adhesion of metal to the inner wall surface of the injection pipe and secondary oxidation of molten steel. It is an object of the present invention to provide a tundish injection tube which is capable of being used.

[0009]

SUMMARY OF THE INVENTION The gist of the present invention is to dispose a molten steel between a ladle and a tundish at a position including a flow of molten steel injected from the ladle into the tundish. And an injection pipe for a tundish which is used by being immersed in molten steel accommodated in the tundish, wherein the injection pipe further comprises (i) 1 or 2 which is built in the peripheral wall portion in the axial direction.
A supply passage of more inert gases, constituting the inner wall surface of the injection tube positioned over the upper and lower near the molten metal surface of the molten steel with communicates with (ii) 1 or 2 or more the supply path, gas blowing A tundish injection tube comprising a possible porous refractory.

[0010] In the present invention, the upper and lower portions of the molten steel surface are 1/4 to 1/4 of the height L of the molten steel centered on the molten steel surface position when the injection tube is immersed in the molten steel in the tundish. 1 /
It is desirable that the thickness be in the range of three times and / or the vertical cross-sectional shape of the inner wall surface of the injection pipe be a tapered shape with a downward expansion of 1/100 to 5/100.

In the above-mentioned present invention, the porous refractory capable of blowing out gas is not limited at all. For example, a porous refractory or a refractory having a large number of through holes having a diameter of about 3 to 7 mm. Can be exemplified. By using this porous refractory material, an inert gas can be blown into the molten steel without causing clogging of the discharge portion due to a jug even when immersed in the molten steel. The number of the inert gas supply paths may be one or two or more, but is preferably two or more in order to suppress the generation of splash or the like.

[0012]

Hereinafter, the present invention will be described in detail together with the functions and effects. The injection pipe for a tundish according to the present invention comprises: (i) one or more inert gas supply paths built in the peripheral wall portion in the axial direction (vertical direction); and (ii) one or more inert gas supply paths. A gas-blowable porous refractory, which communicates with the supply passage and constitutes an inner wall surface of an injection pipe positioned above and below the molten steel surface.

Therefore, from the porous refractory material, an inert gas can be limitedly and partially ejected to the molten steel surface where the oxidation of the molten steel is remarkable and the vicinity of the upper and lower surfaces of the molten steel. A remarkable molten steel sealing effect can be obtained at an inert gas flow rate. At this time, the installation position of the porous refractory in the injection pipe is 1/4 to 1/4 of the injection pipe height L centered on the molten steel surface position when the injection pipe is immersed in the molten steel in the tundish. A range of 1/3 times is desirable in order to achieve the maximum molten steel sealing effect at the minimum inert gas flow rate.

Further, even if the ingot adheres to the inner wall surface of the injection pipe during the injection of molten steel, the ingot is cooled from the lower end to the upper end by the inert gas after the casting is completed, and the ingot is solidified.
Due to the shrinkage, it can be peeled off from the inner wall surface and dropped on the molten steel in the tundish. At this time, it is desirable that the shape of the inner wall surface of the injection pipe be a tapered shape with a downward expansion of 1/100 to 5/100 in order to facilitate peeling of the adhered metal into the molten steel.

By the way, in the injection pipe proposed in Japanese Utility Model Publication No. Sho 60-27580, the number of inert gas outlets to be installed is simply reduced (for example, a plurality of outlets shown in FIG. 3 (a)). Of these, the amount of inert gas used can be reduced by closing other than about four from the bottom.) However, in this case, the amount of inert gas is insufficient to fill the entire inner surface of the injection pipe, and The sealing effect cannot be secured.
In addition, the number of outlets to be installed is reduced, and each outlet is located above and below the molten steel surface, in other words, about four outlets are arranged above and below the molten surface. Then, the outlet immersed in the molten steel is closed by the hot water. In the present invention, the significance of using a porous refractory capable of blowing gas as the gas blowing portion is that such blockage can be eliminated.

Further, the present invention will be described more specifically with reference to the accompanying drawings. FIG. 1A is an overall explanatory view of an example of an apparatus incorporating the injection pipe 14 according to the present invention, and FIG. 1B is an enlarged explanatory view showing a structure of a peripheral wall of an example of the injection pipe 14. Note that the reference numerals in FIG. 1 are the same except that the reference numerals in FIG. 3 are changed from the 30s to the 10s,
In particular, FIG. 1 (a), which is an overall explanatory diagram showing a situation at the time of use, is completely the same as FIG. 3 (a), and therefore, the description of FIG. 1 (a) is omitted.

The injection pipe 14 according to the present invention, which is enlarged in FIG. 1 (b), comprises: (i) a supply path 17 for an inert gas built in the peripheral wall portion in the axial direction; A gas-blowable porous refractory 18 which communicates with the molten steel 15 and constitutes the inner wall surface of the injection pipe 14 located above and below the molten metal surface (indicated by the arrow in FIG. 1B). And The other configuration is not different from the conventionally known injection tube, and thus these two points will be described in detail.

In FIG. 1 (b), the refractory 18 is located near the top and bottom of the molten steel surface of the molten steel 15, preferably at the molten metal position of the molten steel 15 when the injection pipe 14 is immersed in the molten steel in the tundish. , 1 / 4-1 / 3 times the position of the injection tube height L is positioned over (a part in drawing). in this way,
By setting the outlet of the inert gas as the refractory 18 and limiting its installation range, the inert gas atmosphere in the injection pipe 14 can be minimized. A sealing effect can be obtained. In addition, even if metal adhesion is discovered after casting is completed, the lower end of the metal is cooled by inert gas ejected from the refractory and solidification shrinkage occurs, so that the metal is easily separated from the inner surface of the surrounding wall And can be dropped into a tundish.

Other than the part A, ordinary refractories may be used. Generated by oxidation of the molten steel flow in which the molten steel is mainly housed the flow of molten steel collides, the general portion of the injection tube sealing effect of molten steel be filled with an inert gas does not change, necessary for ejecting inert gas Because there is no. However, an inert gas may be used to some extent, but a refractory capable of blowing gas may be used.

Further, according to the present invention, in order to make it easier for the deposited metal to fall after continuous casting with an inert gas, in addition to blowing the inert gas, as shown in part B in FIG. In addition, it is desirable to provide a taper of downward spread on the inner surface of the peripheral wall of the injection pipe 14. By giving a taper,
It is possible to completely eliminate the work of manually removing the adhered metal.

The taper ratio b / a (where a and b are the axial length and the horizontal length of the tapered portion, respectively) is 0.01 to
A range of 0.05 is desirable. If b / a is less than 0.01, the effect of preventing the adhesion of the metal becomes small, while if b / a is more than 0.05, manufacturing troubles increase. In the present invention, the flow rate of the inert gas may be set as appropriate, but under normal operating conditions, the flow rate may be set appropriately within the range of 300 to 2000 l / min according to the quality grade of the steel to be cast.

As described above, according to the present invention, the injection pipe seal sealing technique shown in FIG. 2 and the Japanese Utility Model Publication No. 60-27580 shown in FIG.
Assuming that the Ar flow rate in FIG. 2 is 1 as compared with the technique proposed by the above publication, the inert gas flow rate in FIG. 3 is about 0.5, whereas the inert gas flow rate according to the present invention is about 0.35. The present invention can achieve a sealing effect equivalent to that of the prior art with a small inert gas flow rate, and can quickly respond to seal breakage during continuous casting, so that the secondary oxidation of molten steel by continuous casting is greatly reduced. That the ingot adheres to the inner surface of the injection pipe, the lower end of the injection pipe is cooled by an inert gas, and furthermore, the tape is applied to the inner wall of the injection pipe. Splashes are not present at all because they fall off and fall into the tundish, and the splash scatter caused by turbulence in the molten metal surface, as shown in Japanese Utility Model Publication No. In addition, there is no problem at all due to blowing into the surface only, and there is no sticking of the ingot, so that the ingot cutting operation after continuous casting can be abolished. There was obtained an effect that there was no damage due to fusing and reuse was possible.

Further, the present invention will be described in detail with reference to examples, but this is an exemplification of the present invention, and the present invention is not limited thereto.

[0024]

Embodiment 1 The present inventors used the apparatus shown in FIGS. 1 (a) and 1 (b) to appropriately change the taper ratio b / a, and
A 50 mm tundish injection tube was installed between the ladle and the tundish for continuous casting, and the adhesion of the metal to the inner wall surface of the injection tube was investigated. FIG. 4 shows the results. In the same figure, the metal unfalling rate refers to the rate at which the metal that has adhered to the injection pipe after the end of casting does not fall into the tundish due to cooling and solidification shrinkage,

[0025]

(Equation 1)

Is represented by As is clear from the figure, if b / a is in the range of 0.01 to 0.05, the adhered metal is completely eliminated.

[0027]

Example 2 Four consecutive castings were performed using the injection pipe according to the present invention and the injection pipes shown in FIGS. At this time, the flow rate of the inert gas when the injection pipe shown in FIG.
l / min, and the flow rate of the inert gas in the case of using the injection pipe shown in FIG. 3 is two levels of 2000 and 1400 l / min, and 660 l / min when the injection pipe according to the present invention is used. Met.

At the end of each charge, the inert gas concentration in the vicinity of the molten steel surface in the injection pipe was measured, and the sealing properties of each injection pipe were investigated. The results are shown graphically in FIG. In the same figure, the inert gas concentration in the steady portion is shown. According to the present invention, it was found that good results were continuously obtained regardless of casting, and the sealing property of the injection pipe according to the present invention was remarkable. I understand.

[0029]

Embodiment 3 Continuous casting is performed using the injection pipe according to the present invention and the injection pipes shown in FIGS. 2 and 3, and molten steel in a ladle after RH degassing, which is a process prior to continuous casting [N]. Steel in the tundish when the forging amount is 1/2
[N] was measured. The results are shown graphically in FIG.
From the figure, it can be seen that, according to the present invention, the pickup of [N] in the molten steel between the ladle and the tundish is the same as the conventional one despite the low inert gas flow rate.

[0030]

Embodiment 4 Continuous casting was carried out using the injection pipe according to the present invention and the injection pipes shown in FIGS. 2 and 3, and the T-cast in the mold from the start to the end of continuous casting was obtained for each.
[O] (ppm) and [N] (ppm) were measured to evaluate secondary oxidation of molten steel during continuous casting. The results are shown graphically in FIGS. FIG. 7 is a graph showing T- [O] in the mold over time, and FIG. 8 is a graph showing the ratio of T- [O] and [N] of the steady portion (completely sealed state) and the continuously cast portion. Are plotted on the vertical and horizontal axes, respectively, and the relationship between the two was investigated.

That is, if the values on the vertical and horizontal axes are both 1 or less, it means that secondary oxidation of the cast portion has not occurred successively, and if it is 1 or more, secondary oxidation has occurred. It can be seen from the figure that according to the present invention, secondary oxidation due to seal breakage during continuous casting hardly occurred, and good results were obtained.

[0032]

As described above in detail, according to the present invention, a method for sealing molten steel with an inert gas in an injection pipe is improved.
It became possible to eliminate the adhesion of metal to the injection pipe and the secondary oxidation of molten steel in all cases.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the structure of a tundish injection tube according to the present invention. FIG. 1 (a) shows an injection tube according to the present invention.
FIG. 14 (b) is an overall explanatory diagram incorporating the injection pipe 14;
It is an enlarged explanatory view showing the structure of the peripheral wall portion.

FIG. 2 is an explanatory view showing a structure of a conventional tundish injection tube.

FIG. 3 is an explanatory view showing the structure of a seal pipe proposed by Japanese Utility Model Publication No. 60-27580, wherein FIG. 3 (a) is an overall explanatory view incorporating an injection pipe 34, and FIG. FIG. 4 is an enlarged explanatory view showing a structure of a peripheral wall portion of an injection pipe 34.

FIG. 4 is a graph showing a relationship between b / a and a metal unfalling rate in Example 1.

FIG. 5 is a graph showing the relationship between the state of sealing in an injection pipe and the concentration of inert gas in Example 2.

FIG. 6 is a graph showing the relationship between [N] after RH degassing and [N] in a tundish in Example 3.

FIG. 7 shows casting time and T- [O] in a mold in Example 4.
6 is a graph showing a relationship with the graph.

8 is a graph showing a secondary oxidation state according to a T- [O] ratio and an [N] ratio in Example 4. FIG.

[Explanation of symbols]

11: Ladle 12: Sliding nozzle 12a: Sliding upper nozzle 12b: Sliding upper plate 12c: Sliding lower plate 12d: Sliding lower nozzle 13: Tundish 14: Injection pipe 15: Molten steel 15a, 15b: Splash 16: Injection flow 17: Supply path 18: Outlet 21: Injection pipe 22: Molten steel flow 23: Ring pipe 24: Tundish 25: Sliding nozzle 26: Immersion nozzle 27: Mold 28: Molten steel 31: Ladle 32: Sliding nozzle 32a: Sliding upper nozzle 32b : Sliding upper plate 32c: Sliding lower plate 32d: Sliding lower nozzle 33: Tundish 34: Injection tube 35: Molten steel 35a, 35b: Splash 36: Injection flow 37: Supply path 38: Spout

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-81253 (JP, A) JP-A-61-67959 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 11/10 360 B22D 11/10 320 B22D 41/58

Claims (3)

(57) [Claims] 1. A ladle and a tundish which are arranged at a position including an injection flow of molten steel from the ladle to the tundish inside, and immersed in molten steel accommodated in the tundish and used. A tundish injection tube, further comprising: (i) 1 or 2 which is built in the peripheral wall portion in the axial direction.
Constitute a supply passage of more inert gases, the injection tube wall located over the upper and lower near the molten metal surface of the molten steel with communicates with (ii) 1 or 2 or more the supply path, which can be gas blowing An injection pipe for a tundish, comprising a porous refractory. 2. The upper and lower vicinity is centered on a molten steel surface position when the injection pipe is immersed in molten steel in a tundish.
2. The tundish injection tube according to claim 1, wherein the height of the injection tube is 1/4 to 1/3 times the height of the injection tube. 3. The vertical cross-sectional shape of the inner wall surface is 1/100 to
3. The injection pipe of a tundish according to claim 1 or 2, wherein the injection pipe has a tapered shape of 5/100 downward expansion.