JPH1128553A - Method for supplying molten metal into continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the clogging of an immersion nozzle and the entrapment of mold flux and to improve the stabilization of an operation and the quality of a cast slab by arranging the immersion nozzle so that discharging holes of the immersion nozzle are mutually faced and the discharge flows are mutually faced and do not collide heat-on each other. SOLUTION: Molten metal is supplied into a mold by using two pieces of a first and a second immersion nozzles 1a, 1b having the discharging hole in one direction on side surface to produce the cast slab. The first immersion nozzle 1a and the second immersion nozzle 1b are arranged on the center line Y-Y in the mold thickness in parallel with the mold long sides. The first and the second immersion nozzles 1a, 1b are arranged so that the discharging holes 2a, 2b of both immersion nozzles 1a, 1b and the discharge flows 3a, 3b of molten steel become the parallel faced flows. The spouting angles θa , θb formed between the discharge flows 3a, 3b and the center line Y-Y are set to 2-10 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for feeding molten steel into a mold by means of an immersion nozzle when continuously casting a slab, particularly when casting a wide thin slab.

[0002]

2. Description of the Related Art The simplification and omission of the hot rolling process have been pursued from the viewpoints of saving the manufacturing cost and equipment cost of the hot rolling process and saving energy.

[0003] Therefore, attention has been paid to widening and thinning of slabs. However, recent remarkable advances in refining and casting techniques have made it possible to produce wide and thin slabs of good quality.

[0004] In order to stabilize the operation and quality of continuous casting of wide thin cast slab, the method of hot water supply into the mold has become an important technology.
Various immersion nozzles have been proposed for this purpose.

However, when a mold having a thin slab thickness is used, it is necessary to reduce the thickness of a nozzle immersed in the mold. This is because when the distance between the inner surface of the mold and the immersion nozzle is reduced, the flow of molten steel into the mold becomes unstable, causing problems such as solidification on the molten metal surface and poor slagging of the mold flux.

[0006] Therefore, while the usual immersion nozzle is cylindrical, it is necessary to make the immersion nozzle flat in the production of wide thin cast pieces, as disclosed in Japanese Patent Application Laid-Open Nos. 62-197252 and 62-197252. -292255.

However, as the thickness of the immersion nozzle decreases, the following problems occur in the immersion nozzle itself.

(1) The discharge port width (discharge port cross-sectional area) of molten steel is reduced, and nozzle clogging is likely to occur. When nozzle clogging occurs, the discharge flow rate of molten steel from a plurality of discharge ports of molten steel (a commonly used nozzle has two discharge ports) becomes different from each other, resulting in a single flow phenomenon. When the one-sided flow occurs, the fluctuation of the molten metal level in the mold becomes large, which causes the mold flux to be entrained in the molten steel, causes the solidified shell to become non-uniform, and the like, and deteriorates the quality of the surface of the slab and the inside of the slab.

(2) If the sectional area of the discharge port of molten steel is not sufficient, there is a limit in securing a supply amount of molten steel required for increasing the casting speed.

(3) If the width of the mold is wide, the discharge flow of the molten steel does not reach the vicinity of the short side of the mold, the amount of heat is insufficient, the molten metal surface starts to solidify, and the mold flux is not sufficiently slagged (the inner surface of the mold and the slabs). Insufficient lubrication between the surfaces), breakage of the immersion nozzle, etc. occur, making operation difficult.

As described above, in the conventional hot water supply with one immersion nozzle, when a wide and thin mold is used,
There are limits to stabilizing casting operations, increasing casting speed, and maintaining slab quality.

In order to stabilize a large amount of hot water supplied into a wide and thin mold,
Japanese Patent Application Laid-Open Nos. 8-99155 and 8-192253 disclose a method of supplying hot water in parallel with two immersion nozzles in the width direction in the mold.

According to these methods, the discharge amount of the molten steel from the immersion nozzle can be sufficiently ensured, the flow velocity of the discharge flow in the width direction of the mold and the molten steel temperature become uniform, and the above-mentioned problems that occur during continuous casting of wide thin slabs are obtained. Problem is improved.

However, these methods still have the following problems. Using a plurality of immersion nozzles, shortening the distance between the immersion nozzle and the short side of the mold, and discharging to the short side, while the problem of the discharge amount and the flow rate is improved,
The discharge flow of the molten steel collides with the solidified shell on the short side of the mold, leading to the re-melting of the solidified shell, and furthermore, to the operation problem of breakout. This phenomenon is likely to occur when the casting speed is increased and the amount of hot water is increased, and therefore, the increase in the casting speed is restricted. Therefore, it is necessary to ensure a certain distance or more between the immersion nozzle and the short side of the mold.

On the other hand, when the discharge ports of the molten steel are made to face each other between the immersion nozzles, the discharge flows from both nozzles collide in the central portion between the immersion nozzles, and the level of the molten metal surface greatly changes due to the upward flow after the collision. Become. This fluctuation increases as the casting speed increases, and entrainment of the mold flux occurs, thereby reducing the quality of the slab.

Although the velocity of the collision flow and the upward flow of the molten steel on the solidified shell on the short side of the mold can be reduced to some extent by an electromagnetic brake (a function of controlling the discharge flow of the molten steel by applying a DC magnetic field), the casting speed is reduced. When the discharge flow rate of molten steel increases due to the increase, there is a limit.

[0017]

SUMMARY OF THE INVENTION The present invention relates to a hot water supply method for continuous casting of wide thin cast slabs. More specifically, it is possible to prevent clogging of a dipping nozzle and entrainment of mold flux, thereby stabilizing operation and improving cast slabs. An object of the present invention is to provide an immersion nozzle installation method that can maintain and improve quality.

[0018]

Means for Solving the Problems The present inventors have conducted various experiments and studied and obtained the following findings. Use two immersion nozzles with one molten steel discharge port on the side, place these discharge ports facing each other and install them parallel to the long side of the mold, and select the discharge angle of molten steel as desired Thereby, the collision between the two discharge flows can be avoided, and the fluctuation of the molten metal level between the immersion nozzles can be suppressed.

The present invention has been made based on such findings, and the gist is as follows (1) and (2).

(1) Molten steel is supplied to a mold by using two immersion nozzles each having a discharge port in one direction on a side surface, and when producing cast slabs, the immersion nozzles face each other with the discharge ports facing each other.
A hot water supply method for continuous casting, characterized in that the discharge flows from the discharge ports are arranged in such a manner as to be countercurrent and the discharge flows do not directly collide with each other.

(2) The hot water supply method for continuous casting according to claim 1, wherein the discharge flow from the discharge port is a parallel counterflow having an angle of 2 to 10 ° with respect to the long side of the mold.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for feeding molten steel into a mold using the immersion nozzle of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing an example of the arrangement of an immersion nozzle in a mold according to the present invention and the flow of molten steel formed in this case. As shown in FIG. 1, in the mold cross section, on the center line YY of the mold thickness parallel to the long side of the mold,
Two immersion nozzles 1a and 1b are arranged. Thereafter, the discharge flow of the molten steel is made countercurrent so that the discharge ports 2a, 2b of the molten steel provided in the respective immersion nozzles 1a, 1b face each other. Preferably, the discharge angles θa and θb of the molten steel are made the same with respect to the center line Y-Y of the thickness of the mold, and the discharge flows 3a and 3b of the molten steel are made to flow in parallel countercurrent.

When the molten steel discharge angles θa and θb are selected, the molten steel discharge flow 3a from the discharge port 2a of the first immersion nozzle 1a collides with the molten steel discharge flow 3b of the second immersion nozzle 1b. The swirling flow 5a is formed from the side surface of the second immersion nozzle 1b along the inner surface 4 of the mold without the need. Swirling flow 5
Then, a merges with the molten steel discharge flow 3b of the second immersion nozzle 1b.

In this flow mode, the discharge flow 3 of both molten steels
The upward flow generated by the collision of the nozzles 3a and 3b decreases, and the fluctuation of the molten metal level between the first immersion nozzle 1a and the second immersion nozzle 1b decreases. Furthermore, the continuous swirling flow 5a, 5b of molten steel promotes the detachment of air bubbles and non-metallic inclusions once trapped in the solidified shell, thereby improving the surface quality of the cast slab.

The reason why the discharge angle θ of the molten steel, that is, the discharge flow from the discharge port of the molten steel in the present invention is limited as described above will be described below.

FIG. 2 shows the relationship between the molten steel discharge angle θ and the molten metal surface fluctuation amount. As shown in FIG. 2, the discharge angle θ of molten steel is 2
If it is less than °, depending on the size of the discharge port, the distance between the immersion nozzles, etc., the collision of the discharge flows 3a and 3b will cause the molten steel to rise, causing the molten metal level fluctuation to exceed 5 mm at the maximum amplitude, and entrainment of the mold flux will occur. It is preferable to set the angle to 2 ° or more because the quality of the cast slab may be reduced. Also 10
°, the level fluctuation in the mold is 3mm at the maximum amplitude
However, the collision of the molten steel discharge flows 3a and 3b with the solidified shell on the long side of the mold becomes large, and in some cases, the solidified shell re-dissolves in that portion, causing a breakout. desirable. More preferably, it is 3 to 7 degrees.

The shape of the immersion nozzle is preferably about 100 to 500 mm in width and about 30 to 70 mm in thickness in the cross section.
However, even within this range, it is preferable to select an optimum value in consideration of the cross-sectional size of the mold. It is important to avoid the flow of the molten metal in the mold. For this reason, it is desirable that the distance be as small as possible and that the distance between the immersion nozzle and the long side of the mold be 10 mm or more.

The thickness of the immersion nozzle is preferably about 5 to 20 mm. It is only necessary to have the necessary strength against thermal shock and thermal stress, and it is not necessary to make it thicker.

FIG. 3 shows an embodiment of the immersion nozzle of the present invention. In order to set the discharge angle θ of the molten steel, as shown in FIG. 3A, when the angle of the immersion nozzle and the discharge angle coincide with each other, the molten steel may be provided by rotating the entire immersion nozzle. As shown in (b), while the immersion nozzle body is kept parallel to the long side of the mold, the discharge angle may be adjusted by giving an angle θ only to the discharge port of molten steel. Note that FIG.
The immersion nozzle of (a) is not necessarily the center line Y-Y of the mold thickness.
It is needless to say that the molten steel jet port may have an angle θ with respect to the long side of the mold even if it is not installed above. Further, as shown in FIG. 3 (c), the molten steel discharge port of the immersion nozzle has no angle θ, so that counterflows are parallel to the long sides of the mold and the discharge flows do not directly collide with each other. It may be installed in.

As shown in FIGS. 6 (a), 6 (b) and 6 (c), which will be described later, the discharge angle of the molten steel in the vertical cross section may be substantially the same as the discharge angle of the molten steel of a commonly used immersion nozzle. A downward angle of 30 to 60 degrees with respect to the horizontal is common.

FIG. 6 is an enlarged vertical sectional view of the molten steel discharge port observed in the immersion nozzle. (A) and (b) of FIG.
FIG. 3C shows an example of a submerged nozzle used in the method for supplying a wide thin cast slab according to the present invention. FIG. Each downward angle is 30 to 60 degrees.

Further, in order to maintain the symmetry in the width direction of the molten metal flow and the molten metal surface fluctuation, the molten steel discharge angle θa,
θb is preferably set to the same value for both immersion nozzles.

The immersion depth of the immersion nozzle in the molten steel may be approximately the same as the normal range, generally in the range of 100 to 500 mm, and preferably the same value for both immersion nozzles.

To suppress the fluctuation of the molten metal level, it is more effective to apply an electromagnetic brake to the discharge flow of the molten steel. However, the strength is selected in the range of 2000 to 6000 G, and it is preferable to increase the strength as the casting speed increases. .

[0036]

EXAMPLE A low-carbon aluminum-killed steel was supplied at a speed of 5.0 m / min by a two-strand curved continuous casting machine.
A wide thin slab having a thickness of 100 mm and a width of 2000 mm was produced.

At the time of casting, the maximum amplitude was measured as the amount of fluctuation of the molten metal level in the mold, the state of suppression of the fluctuation of the molten metal level was visually observed, and the surface cleanness of the slab was examined.

Investigation of the surface cleanliness of the cast slab after casting revealed that the total length was 1
After scarfing the surface of the slab to 3 mm below the surface of the slab of 0 m slab, it was cleaned with a grinder and JIS G0
Samples were taken according to 555 (microscopic test method for non-metallic inclusions in steel). The evaluation of the surface cleanliness of the slab is
The best condition was A and the worst condition was E.

(Example 1) Low carbon killed steel (% by weight,
C: 0.06, Si: 0.050, Mn: 0.25,
(P: 0.015, S: 0.004, Al: 0.043)
No. In one strand, as Example 1 of the present invention, two immersion nozzles were used, and the discharge angle θ of the molten steel with respect to the long side of the mold was set to 0 °. On the other hand, No. In the second strand, as Comparative Example 1, two conventional immersion nozzles were used. Table 1 shows the hot water supply conditions and the results.

FIG. 4 is a schematic cross-sectional view when two immersion nozzles are arranged in a mold. Figures (a) and (c)
Shows the situation of the example of the present invention, and FIG. 3B shows the situation of the comparative example.

Inventive Example 1 was carried out in the manner shown in FIG. 4C, and Comparative Example 1 was carried out in the manner shown in FIG. 4B.

The immersion nozzles used in the examples of the present invention and the comparative examples are those shown in FIG. 6A, and the same applies to the following.

In Example 1 of the present invention produced under the conditions defined in the present invention, the fluctuation amount of the molten metal level in the mold was 3 mm at the maximum amplitude, and the slab surface cleanliness index was as good as B.

However, in Comparative Example 1 out of the conditions defined in the present invention, the fluctuation amount of the molten metal level in the mold was 6 mm at the maximum amplitude, and the slab surface cleanliness index was D.

Therefore, in Example 1 of the present invention, the slab surface cleanliness index was improved as compared with Comparative Example 1 because the fluctuation of the molten metal level in the mold was suppressed.

[0046]

[Table 1]

Example 2 Low carbon aluminum killed steel (% by weight, C: 0.05, Si: 0.054, Mn: 0.2)
2, P: 0.016, S: 0.003, Al: 0.04
No. 7). In the case of the first strand, as Example 2 of the present invention, hot water was supplied using two immersion nozzles and the arrangement shown in FIG. On the other hand, No. In the second strand, as Comparative Example 2, two conventional immersion nozzles having discharge ports in both directions were used. Table 1 shows the hot water supply conditions and the results.

In Example 2 of the present invention produced under the conditions defined in the present invention, the fluctuation amount of the molten metal level in the mold was 3 mm at the maximum amplitude, and the slab surface cleanliness index was as good as B.

However, in Comparative Example 2, which deviated from the conditions defined in the present invention, the fluctuation of the molten metal level in the mold was 6 mm at the maximum amplitude, and the slab surface cleanliness index was C.

Therefore, in Example 2 of the present invention, the fluctuation of the molten metal level in the mold was suppressed, so that the slab surface cleanliness index was improved as compared with Comparative Example 2.

Example 3 Low carbon aluminum killed steel (% by weight, C: 0.05, Si: 0.052, Mn: 0.2
4, P: 0.018, S: 0.005, Al: 0.03
No. 9). In one strand, as Example 3 of the present invention, two immersion nozzles were used and the discharge angle θ of the molten steel with respect to the long side of the mold was set to 8 ° in the arrangement shown in FIG. On the other hand, No. 2
As a comparative example 3, a single immersion nozzle having discharge ports in both directions was used as the comparative example 3 in the arrangement shown in FIG. Table 1 shows the hot water supply conditions and the results. FIG. 5 is a schematic cross-sectional view when one immersion nozzle is disposed in the mold. The immersion nozzle at this time is shown in FIG.
(C).

In Example 3 of the present invention produced under the conditions specified in the present invention, the fluctuation of the molten metal level in the mold was 3 mm at the maximum amplitude, and the slab surface cleanliness index was B.

On the other hand, in Comparative Example 3, in which one immersion nozzle deviating from the conditions stipulated in the present invention was used, the variation in the level of the molten metal in the mold was 3 mm at the maximum amplitude. Was worse.

However, in Comparative Example 3, the fluctuation of the molten metal level
However, since the surface of the molten metal became skinned (solidified) in the vicinity of the short side of the mold and the slag condition of the mold flux was poor, a vertical crack having a length of about 10 to 500 mm was formed on the slab surface. Was visually observed.

[0055]

According to the present invention, fluctuations in the molten metal level in the mold can be suppressed, clogging of the immersion nozzle, entrainment of the mold flux, and re-dissociation of bubbles, nonmetallic inclusions, etc. trapped in the solidified shell can be promoted. Stabilization and maintenance and improvement of slab quality.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of the arrangement of an immersion nozzle in a mold according to the present invention and the flow of molten steel formed in this case.

FIG. 2 is a graph showing the relationship between the molten steel discharge angle θ and the amount of fluctuation in the molten metal level.

FIG. 3 is a schematic diagram showing the relationship between the molten steel discharge port of the immersion nozzle and the discharge angle θ, wherein FIG. 3 (a) shows the angle of the immersion nozzle and FIG. 3 (b) shows the angle of the molten steel discharge port. FIG. 3 (c) is a schematic view in each case where the molten steel discharge angle θ is 0 °.

FIG. 4 is a schematic cross-sectional view of a case where two immersion nozzles are arranged in a mold, and FIG.
FIG. 2B shows the situation of the comparative example, and FIG. 2C shows the situation of the example of the present invention.

FIG. 5 is a schematic cross-sectional view when one immersion nozzle is arranged in a mold.

FIG. 6 is an enlarged vertical sectional view of a molten steel discharge port of the immersion nozzle. FIGS. 6A and 6B are examples of an immersion nozzle used in the method for supplying a wide thin cast slab according to the present invention. Figure (c)
It is an example of a conventionally used immersion nozzle.

[Explanation of symbols]

 YY: center line of mold thickness, 1a: first immersion nozzle, 1b: second immersion nozzle, 2a: discharge port, 2b: discharge port, 3a: discharge flow, 3b: discharge flow, 4: mold inner surface, 5a 5b: swirl flow, θa: discharge angle, θb: discharge angle.

Claims (2)

[Claims] 1. When molten steel is supplied to a mold by using two immersion nozzles each having a discharge port in one direction on a side surface, and a slab is manufactured, the immersion nozzles face each other, and the discharge ports face each other.
A hot water supply method for continuous casting, characterized in that the discharge flows from the discharge ports are arranged in such a manner as to be countercurrent and the discharge flows do not directly collide with each other. 2. The hot water supply method for continuous casting according to claim 1, wherein the discharge flow from the discharge port is a parallel counterflow having an angle of 2 to 10 ° with respect to the long side of the mold.