JP2003251441A - Facility and method for continuously casting molten metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a facility and a method for continuously casting molten metal and for realizing casting a cast slab which is suitable for a base material for producing a pipe, a bar, etc., and has a small ratio of long-side to short-side with high quality and high productivity. <P>SOLUTION: The continuous casting is applied to the molten metal M in the facility for continuously casting the molten metal in which a ratio W/T between the width W of the long-side 1b and the width T of the short-side 1a constituting a mold 1, is set to 2-3.5 and also, an immersion nozzle 2 has a first spouting holes 2a for molten metal M formed on a side wall 21 faced to the short-sides 1a in the mold 1 and a second spouting hole 2b for molten metal M formed at a bottom wall 2 faced to the bottom side of the mold 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting facility and method for continuous casting of molten metal, and more particularly, to a slab having a small ratio of a long side of a mold and a short side of a mold applicable as a material such as a pipe or a rod. It relates to a technique effective for casting.

[0002]

2. Description of the Related Art In a continuous casting facility for casting molten metal, when molten metal is supplied from a tundish into a mold through a dipping nozzle, the molten metal solidifies due to heat removal from the mold to form a solidified shell. It is formed. At this time, the mold powder supplied on the surface of the molten metal in the mold is melted by the heat from the molten metal, so that it penetrates into the gap between the mold and the solidified shell and causes friction between the mold and the solidified shell. Plays a role to reduce.

Here, in a slab continuous casting facility for casting a slab having a flat rectangular cross section, as shown in FIG. 4, since the ratio of the long side 10b to the short side 10a of the mold 10 is large, a pair of short sides is formed. Sidewalls 21 respectively facing the sides 10a
A two-hole immersion nozzle 20 having a discharge hole 20a at 0 is used. The molten metal M jetted from each of the two-hole immersion nozzles 20 toward the short side 10a side collides with the short side 10a to form an upwardly reversed flow, so that on the molten metal M bath surface in the mold 10. It promotes heat transfer to the mold powder (not shown) present in the, and maintains its proper melting.

As a continuous casting facility for casting molten metal, in addition to the slab continuous casting facility described above, a bloom for casting a bloom or billet having a substantially square cross section, which is a raw material for manufacturing pipes, rods, etc. Continuous casting equipment and billet continuous casting equipment are known. However, it is not economical to have a variety of continuous casting equipment from a slab continuous casting equipment to a billet continuous casting equipment in a factory that performs high-mix low-volume casting. For this reason, slabs applicable as raw materials such as pipes and rods have been cast using slab continuous casting equipment.

At this time, in order to make the slab cast by the slab continuous casting equipment have a cross-sectional shape as close as possible to a bloom or billet, the long side width W is larger than that of the plate slab.
Is made narrower so that the cross-sectional shape of the slab is closer to a ratio W / T of the long side width W and the short side width T (hereinafter referred to as long / short side ratio) to 1, but if this ratio is too small, Since the mold cross-sectional area becomes small, productivity is impaired. Therefore, it is possible to increase the casting speed, but if the casting is done too fast, the slab will be pulled out from the mold without the solidified shell developing sufficiently in the mold. (This is called bulging) and the quality of the slab is impaired, or there is a problem that the solidified shell breaks and molten metal deviates from the inside, so-called breakout occurs, making operation difficult. .

In view of this, due to such restrictions on the material and restrictions on the casting speed, conventionally, the long / short side ratio W / T is set to 2
~ 3.5 (Normally W / T = 4 for slabs for plate materials)
Of a slab that can be applied as a material for producing pipes and rods under the condition that the casting speed of the slab is about 1 to 1.2 times the speed for producing a slab for plate materials. Casting is taking place.

[0007]

However, when the molten metal is supplied to such a mold through the above-mentioned two-hole immersion nozzle which is applied in the ordinary slab continuous casting equipment, the injection hole of the immersion nozzle is used. Since the distance to the short side is short, the collision flow velocity of the molten metal on the short side is too high. For this reason, since the heat supply to the short side becomes large, the thickness of the solidified shell on the short side becomes smaller than that on the long side, and bulging of the cast piece due to the static pressure of the molten metal occurs. There was a problem.

In this case, by reducing the casting speed,
A means for suppressing the bulging by increasing the thickness of the solidified shell on the short side has been proposed, but there is a problem that the productivity is not good. Further, by increasing the amount of cooling water, a means for increasing the thickness of the solidified shell on the short side and suppressing the bulging of the slab has been proposed, but an increase in the amount of cooling water may cause surface cracking. There is a problem that the quality of the cast piece is adversely affected.

Therefore, the present invention has been made in view of the above circumstances, and is capable of producing, with high quality and high production efficiency, a slab with a small long-to-short side ratio applicable as a raw material for producing pipes and rods. An object of the present invention is to provide a continuous casting facility and a continuous casting method for a castable molten metal.

[0010]

In order to solve such a problem, the continuous casting equipment of the present invention is a casting mold comprising a pair of long sides and a pair of short sides, molten metal through a dipping nozzle. In a continuous casting facility for supplying and continuously casting molten metal, the ratio W / T of the width W of the long side and the width T of the short side forming the mold is 2-3. 5, the immersion nozzle has a first discharge hole of molten metal formed in a side wall facing the short side of the mold, and a molten metal formed in a bottom wall facing the bottom side of the mold. It is characterized by having a second discharge hole.

Here, continuous casting of molten metal according to the present invention
In the manufacturing equipment, the area of the second discharge hole is S₁And soak
The flow passage cross-sectional area of the molten metal in the nozzle is S₂And
S, ₁<S₂To be satisfied with the relationship
Yes. In addition, in the continuous casting facility for molten metal in the present invention,
And contains 2 to 20% by mass of Cr as a molten metal.
It is preferable that molten steel for seamless steel pipe material is cast.
Yes.

The continuous casting method for molten metal according to the present invention is a continuous casting method for molten metal in which a molten metal is supplied through a dipping nozzle into a mold having a pair of long sides and a pair of short sides for continuous casting. A casting method, wherein as the mold, a ratio W / T of the width W of the long side and the width T of the short side is 2 to
3.5 as the immersion nozzle, the first discharge hole of the molten metal formed in the side wall facing the short side of the mold and the bottom wall facing the bottom side of the mold as the immersion nozzle. And a second discharge hole for molten molten metal.

Here, continuous casting of molten metal according to the present invention
In the manufacturing method, the area of the second discharge hole is S₁And soak
The flow passage cross-sectional area of the molten metal in the nozzle is S₂And
S, ₁<S₂Use a dipping nozzle that satisfies the relationship
Preferably. In addition, the series of molten metals in the present invention
In the continuous casting method, as a molten metal, 2 to 20 mass%
Of molten steel for seamless steel pipe material containing Cr
And are preferred.

According to the continuous casting equipment of the present invention, the ratio (W / T) of the width W of the long side and the width T of the short side forming the mold is
2 to 3.5, the immersion nozzle has a first discharge hole of molten metal formed in the side wall facing the short side of the mold, and a molten metal formed in the bottom wall facing the bottom side of the mold. By having the second discharge hole of, the discharge of the molten metal to the short side is suppressed, so that the thickness of the solidified shell formed on the short side is secured, and the occurrence of bulging on the slab is prevented. It becomes possible to suppress. Therefore, it becomes possible to cast a slab having a small ratio of the long side to the short side of the mold with high quality and high production efficiency.

Further, according to the continuous casting equipment of the present invention,
The area of the second discharge hole in the pickling nozzle is S₁And soak
The flow passage cross-sectional area of the molten metal in the nozzle is S₂And
S, ₁<S₂Melting by satisfying the relationship
Prevents metal from flowing out only from the second discharge hole,
It is possible to secure the outflow from one discharge hole. Yo
The mold part supplied on the molten metal bath surface in the mold.
Since heat transfer to the wood is ensured,
It is possible to reduce friction between the two.

Further, according to the continuous casting equipment of the present invention,
2 to 2 that cracking defects are likely to occur due to bulging
Even molten steel for a seamless steel pipe material containing 0 mass% of Cr can be cast with high quality and high production efficiency. According to the continuous casting method for molten metal in the present invention, as the mold, the ratio (W / T) of the width W of the long side and the width T of the short side is 2 to 3.5, and As a dipping nozzle, it has a first discharge hole for molten metal formed on the side wall facing the short side of the mold and a second discharge hole for molten metal formed on the bottom wall facing the bottom side of the mold. By using a molten metal, the discharge of molten metal to the short side is suppressed, so the thickness of the solidified shell formed on the short side can be secured and the occurrence of bulging on the slab can be suppressed. Becomes Therefore, it becomes possible to cast a slab having a small ratio of the long side to the short side of the mold with high quality and high production efficiency.

Further, continuous casting of molten metal in the present invention
According to the method, as the immersion nozzle, the area of the second discharge hole
To S₁And the cross-sectional area of the molten metal channel in the immersion nozzle
To S ₂When, S₁<S₂To satisfy the relationship of
By using the molten metal only the second discharge hole
Outflow from the first discharge hole
It becomes possible to secure. Therefore, the molten metal in the mold
Ensures heat transfer to the mold powder supplied on the bath surface
Reduce the friction between the mold and the solidified shell.
And are possible.

Further, according to the method for continuously casting molten metal according to the present invention, even if the molten steel for a seamless steel pipe material containing 2 to 20% by mass of Cr, which is particularly prone to crack defects due to bulging, It is possible to perform casting with high quality and high production efficiency.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the structure of a continuous casting facility according to the present invention, in which (a) is a plan sectional view,
(B) is a front sectional view. The continuous casting method of the molten metal in the present embodiment has, for example, a slab continuous casting facility that has a flat cross-sectional shape and forms a slab that is a material of a plate-shaped metal product, and changes its mold and immersion nozzle. Thus, it is applied to cast a slab that has a substantially square cross-sectional shape and is a material such as a pipe or a rod.

As shown in FIG. 1, the continuous casting equipment used in this continuous casting method for molten metal has a ratio W / T of the width W of the long side 1b and the width A of the short side 1a of 2-3. A mold 1 having a long / short side ratio of 5 and a dipping nozzle 2 installed in the mold 1 are provided. In the figure, 3 is a solidified shell formed during continuous casting of molten metal, and 4 is a support roll for holding a slab on the short side. The continuous casting machine in this continuous casting facility may be any continuous casting machine of a type that supplies molten metal from above the mold, for example, a vertical continuous casting machine, a vertical bending continuous machine. A casting machine, a full-curve continuous casting machine, etc. are mentioned. In particular, it is preferable to use a vertical bending continuous casting machine that avoids inclusion defects and is optimal for high-speed casting.

Here, the width W of the long side 1b constituting the mold 1
When the ratio W / T between the width T of the short side 1a and the width T is less than 2,
Since the cross-sectional area of the mold 1 becomes too small, it becomes difficult to secure high productivity. On the other hand, if the ratio of the width W of the long side 1b and the width T of the short side 1a forming the mold 1 and the ratio W / T exceeds 3.5, it is often used for rolling from a slab to products such as pipes and bars. Energy is required, and if a slab is width-divided by a gas cutter or the like in order to avoid this, the yield due to cutting is reduced, resulting in an increase in cost. For the above reasons, it is preferable that the ratio of the width W of the long side 1b and the width T of the short side 1a that constitute the mold 1 be 2 to 3.5.

The immersion nozzle 2 is composed of a hollow cylinder or the like for supplying the molten metal M from the tundish (not shown) into the mold 1, and the side walls 21 facing the respective short sides 1a of the mold 1. Of the molten metal M formed on the bottom wall 22 of the mold 1 and the bottom wall 22 facing the bottom side of the mold 1 (the lower side in FIG. 1B). 2b and.

Here, a pair or a plurality of pairs of the first discharge holes 2a are formed in parallel with the long side 1b of the mold 1 and on the short side 1a side of the pair of molds 1 as a reference. At this time, the total area of the first ejection holes 2a formed in the side wall 21 opposed to the one short side 1a side (for example, the first ejection hole 2a is formed in the side wall 21 opposed to each short side 1a side). When the holes are formed one by one, it is the area of one hole formed in one of the side walls 21, and two holes are formed in each of the side walls 21 facing the short side 1a of the first discharge hole 2a. If formed, it refers to the total area of the two holes formed in one of the side walls 21), and is 0.5 to 1.2 of the flow passage cross-sectional area S ₂ of the molten metal M in the immersion nozzle 2. It is preferable to double the number.

The first discharge hole 2a is preferably formed so as to have a discharge angle above the horizontal in order to properly supply heat to the bath surface in the mold 1. The second discharge hole 2b has an area smaller than the flow passage cross-sectional area S ₂ of the molten metal M in the immersion nozzle 2 so that the molten metal M from the immersion nozzle 2 can flow out from the first discharge hole 2a. S
To have _one .

Here, the flow passage in the immersion nozzle 2 indicates a portion indicated by 23 in FIG. 1, and the flow passage cross-sectional area S ₂
Indicates the cross-sectional area, that is, the area of the flow path 23 in FIG. According to the continuous casting facility in this embodiment, the width W of the long side 1b and the short side 1a of the mold 1 are
Has a ratio W / T of 2 to 3.5 and is formed on the side wall 21 facing the short side 1a of the mold 1 in the immersion nozzle 2 for supplying the molten metal M to the mold 1. A first discharge hole 2a for the molten metal M, and a second discharge hole 2b for the molten metal M formed on the bottom wall 22 facing the bottom side of the mold 1.
Since the discharge of the molten metal M to the short side 1a side is suppressed, the thickness of the solidified shell 3 formed on the short side 1a side can be secured. Therefore, no bulging is observed in a slab having a small ratio of the long side 1b to the short side 1a of the mold 1, for example, a slab similar to a bloom or a billet applicable as a material such as a pipe or a rod. It becomes possible to perform casting with high quality and high production efficiency.

[0026]

Next, the effects of the present invention will be verified by the following examples and comparative examples. Here, 0.10% produced by a converter and a VOD furnace together with the examples and comparative examples
C, 9.0% Cr, 1.0% Mo steel (where% is% by mass) is continuously cast to obtain a long side width W750 mm and a short side width T26.
A 0 mm (ie, W / T 2.88) slab was produced. Since this steel type is particularly prone to crack defects on the short side due to bulging, it has been conventionally cast at a drawing speed of 0.75 m / min.

In the embodiment, the immersion nozzle has an inner hole diameter of 8
5mmφ, the first discharge hole with two 68 × 48mm holes formed on the side wall facing the mold short side, and the bottom wall facing the mold bottom side with an inner diameter of 3 mm.
A 3-hole nozzle having a second discharge hole formed with 6 mmφ was applied. Here, the area of the second discharge hole / the area of the inner hole of the immersion nozzle (S ₁ / S ₂ ) is 0.18, and the first discharge hole forms an angle of 5 ° upward with respect to the horizontal. So formed.

Using such an immersion nozzle, a drawing speed of 0.75 m / min, 0.85 m / min, 0.9
Casting was performed at 5 m / min and 1.05 m / min, and the maximum bulging amount (m
m) and the rate of occurrence of internal cracks (mm ^-1 ) below the surface of the short side were measured. In addition, the internal crack below the surface of the short side is the sum of the crack lengths (mm) below the surface of the short side observed by P-printing of the transverse section (cut surface perpendicular to the casting direction) of the slab across the slab. It is a value divided by the area (mm ² ). This result is shown in FIG.
And shown in FIG.

On the other hand, in the comparative example, as an immersion nozzle, the inner hole diameter was 85 mmφ, and the contrast was 6 in two directions toward the shorter side of the mold.
A two-hole nozzle having a first discharge hole opened in an area of 8 × 48 mm was applied. Using such an immersion nozzle, casting at the same drawing speed as in the example,
Maximum bulging amount (mm) on the short side of the slab after leaving the mold
And the rate of occurrence of internal cracks (mm ^-1 ) under the short side surface layer were measured. The results are shown in FIGS. 3 and 4.

As shown in FIG. 2, in the comparative example, the bulging amount increases in proportion to the drawing speed,
In this embodiment, the drawing speed is 1.05 m / mi.
Even if it was increased to n, the bulging could be kept below the value of the drawing speed of 0.75 m / min in the comparative example. Further, as shown in FIG. 3, in the comparative example, internal cracking increased in proportion to the drawing speed, but in the present example, the drawing speed was 1.05 m /
Even if it was increased to min, the internal crack could be kept below the value of the drawing speed of 0.75 m / min in the comparative example.

From the above results, by using the immersion nozzle of the present invention, even if the drawing speed is 1.05 m / min, which is 1.4 times the conventional drawing speed, the slab bulging and internal cracking are prevented. With stable and stable operation,
It was confirmed that a slab of good quality could be cast.

[0032]

As described above, according to the continuous casting facility for molten metal in the present invention, the ratio W / T of the width W of the long side and the width T of the short side of the mold is 2 to. In addition to 3.5, the immersion nozzle has a first discharge hole for molten metal formed on the side wall facing the short side of the mold and a first discharge hole for molten metal formed on the bottom wall facing the bottom side of the mold. By having the two discharge holes, it becomes possible to cast a slab having a small long-to-short side ratio applicable to a material for manufacturing a pipe, a rod or the like with high quality and high production efficiency.

According to the continuous casting method for molten metal of the present invention, by using the continuous casting equipment of the present invention, a slab having a small long-to-short side ratio applicable to a material for producing pipes, rods, etc. can be obtained. It becomes possible to perform casting with high quality and high production efficiency.

[Brief description of drawings]

FIG. 1 shows an example of the structure of a continuous casting facility according to the present invention, in which (a) is a plan sectional view and (b) is a front sectional view.

FIG. 2 is a diagram showing a relationship between a drawing speed when a cast piece is drawn from a mold in a continuous casting facility and a maximum bulging amount on a short side of the mold.

FIG. 3 is a diagram showing a relationship between a drawing speed when a cast piece is drawn from a mold in a continuous casting facility and an internal crack occurrence rate under a surface layer of a short piece of the mold.

FIG. 4 shows a configuration example of a conventional continuous casting facility,
(A) is a plane sectional view and (b) is a front sectional view.

[Explanation of symbols]

1,10 mold 2, 20 immersion nozzle 21, 210 Side wall of immersion nozzle 22 Bottom wall of immersion nozzle 23 Flow path in immersion nozzle 2a, 20a First discharge hole 2b Second discharge hole 3, 30 solidified shell 4,40 Support roll for holding slab M molten metal

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Eiji Tawara             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Chiba Steel Works, Ltd. F-term (reference) 4E014 DB03

Claims (6)

[Claims] 1. A continuous casting facility for molten metal, wherein molten metal is supplied through an immersion nozzle into a mold consisting of a pair of long sides and a pair of short sides to continuously cast the molten metal. The width W of the long side and the width T of the short side constituting
And the immersion nozzle has a ratio W / T of 2 to 3.5, and the immersion nozzle has a first discharge hole of molten metal formed in a side wall facing the short side of the mold and a bottom side of the mold. And a second discharge hole for the molten metal formed in the bottom wall facing to the continuous casting facility for the molten metal. 2. The area of the second discharge hole is S _1, and the flow passage cross-sectional area of the molten metal in the immersion nozzle is S ₂
The continuous casting facility for molten metal according to claim 1, wherein the relationship S ₁ <S ₂ is satisfied. 3. The continuous casting facility for molten metal according to claim 1, wherein molten steel for a seamless steel pipe material containing 2 to 20 mass% of Cr is cast as the molten metal. . 4. A continuous casting method for a molten metal, wherein molten metal is supplied through an immersion nozzle into a mold consisting of a pair of long sides and a pair of short sides to continuously cast the molten metal. , A width W of the long side and a ratio W / T of the width T of the short side of 2 to 3.5 are used, and as the immersion nozzle, a side wall facing the short side of the mold. A molten metal having a first discharge hole of the molten metal formed in the mold and a second discharge hole of the molten metal formed in the bottom wall facing the bottom side of the mold. Continuous casting method. As claimed in claim 5, wherein the immersion nozzle, the area of the second discharge holes and S _1, the flow path cross-sectional area of the molten metal in the immersion nozzle when the S _2, the relationship of S ₁ <S ₂ 5. Use of a satisfying one.
The method for continuous casting of molten metal according to. 6. The continuous casting method for molten metal according to claim 3, wherein molten steel for a seamless steel pipe material containing 2 to 20 mass% of Cr is cast as the molten metal.