JP2790420B2 - Carbon steel slab by twin roll continuous casting and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the production of carbon steel slabs by twin roll continuous casting.

[0002]

2. Description of the Related Art FIG.
FIG. 1 is an explanatory view of a twin-roll type continuous casting described in Japanese Patent Laid-Open Publication No. H10-209,878. Two casting rolls 1-1 and 1-2 which are arranged in parallel and horizontally to rotate in the direction of arrow 8 are arranged at intervals corresponding to the plate thickness tmm of the slab 6 to be manufactured. Side dams 12 (12 ') are arranged at both ends of the casting roll in close contact with the side surfaces of the casting rolls 1-1 and 1-2. When the molten metal 5 is poured into the pool 2 formed by the upper part of the casting roll and the side dam,
The molten metal forms solidified shells 3-1 and 3-2 on the surface of the casting roll, and the solidified shells 3-1 and 3-2 grow while moving in the direction of arrow 8 following the rotation of the casting roll. From the minimum gap (kiss point) 4 between the rolls 1-1 and 1-2 to the slab 6
It is taken out as.

FIG. 3 is an explanatory view of a twin-roll type continuous casting using a contact limiting plate 9. In this case, the contact limiting plate 9 is disposed with its lower end 10 close to the surfaces of the casting rolls 1-1 and 1-2, and the contact limiting plate and the side weir (not shown; see FIG. 2).
The molten metal 5 is poured into the basin 2 formed by the above steps.

In the example of FIG. 2, since the formation of the solidified shells 3-1 and 3-2 starts on the bath surface 7 of the molten metal, if scum or the like is floating on the bath surface 7 of the molten metal, the scum is formed. It is wrapped between the molten metal and the drum, so that the cooling by the drum becomes uneven and there is a problem that scum flaws and cracks occur on the surface of the slab. In the example of FIG. 3, the formation of the solidified shells 3-1 and 3-2 starts below the molten metal bath surface 7, for example, at 11. Therefore, even when scum or the like floats on the bath surface 7 of the molten metal, the scum or the like is not caught between the molten metal and the drum, and generation of scum flaws and cracks can be effectively prevented.

[0005]

According to the twin-roll type continuous casting shown in FIGS. 2 and 3, a plate-like carbon steel slab having a thickness of 0.5 to 6 mm can be produced. The rolling process can be greatly simplified. However, according to the findings of the present inventors, carbon steel slabs produced by the method shown in FIGS. 2 and 3 without any special ingenuity show that the slabs have coarse crystal grains and therefore have insufficient ductility. There is a problem. An object of the present invention is to provide a carbon steel slab having fine crystal grains and a method for producing the same.

[0006]

The present inventors have found that in the continuous casting method shown in FIG. 3, when the position of the contact limiting plate 9 is changed, the size of the primary crystal of the obtained slab 6 changes. And obtained the present invention.

That is, in the present invention, when performing twin-roll continuous casting using the contact limiting plate 9, the lower end 10 of the contact limiting plate 9 is cast at least 20 mm below the molten metal bath surface 7 and from the bath surface. The carbon steel slab is set above the depth of 3/4 of the roll radius, and at the same time, the distance between the lower end of the contact limiting plate and the surface of the casting roll 3-2 is kept at 0.1 mm or more and 1 mm or less. Casting.

FIG. 1 shows the crystal grains of a slab when the set depth of the contact limiting plate is changed while the distance between the lower end 10 of the contact limiting plate and the surface of the casting roll is maintained at 0.1 mm or more and 1 mm or less. It is a figure which shows the magnitude of. The thickness of the slab was 1.
5 mm to 6 mm. The size of the crystal grain is 1/4 of the plate thickness from the surface by macro-etching the vertical section of the slab with picric acid.
The thickness range was examined with a 100 × optical micrograph.
This is the average value of the size of the crystal grains in the zero visual field.

As shown in FIG. 1, when the lower end of the contact limiting plate is arranged at least 20 mm below the bath surface, the crystal grains of the slab are remarkably refined. However, if it is arranged at a depth exceeding 3/4 of the radius of the casting roll from the bath surface, the growth of the solidified shell is insufficient, and the slab is easily broken immediately below the casting roll. Therefore, in the present invention, the lower end of the contact limiting plate is disposed below 20 mm below the bath surface and above 3/4 of the radius of the casting roll.

In the present invention, the gap between the lower end of the contact limiting plate and the surface of the casting roll is set to 0.1 mm to 1.0 mm. If the gap is less than 0.1 mm, the contact limiting plate comes into contact with the drum due to deformation due to heat from the molten metal, the contact limiting plate wears, and the contact limiting plate made of refractory comes into contact with the surface of the casting roll. Causes numerous flaws on the roll surface. If the gap between the lower end of the contact limiting plate and the surface of the casting roll exceeds 1.0 mm, molten metal is poured into this gap, and the surface properties of the cast slab are impaired.

The lower end of the contact limiting plate is set at 20 mm below the bath surface of the molten metal.
If it is set lower than this, the reason why the metal structure of the slab becomes finer is not necessarily clear, but is presumed as follows. That is, when there is no contact limiting plate or when the lower end 10 of the contact limiting plate is above 20 mm below the bath surface of the molten metal, the casting roll 1-1 in FIGS. 2 is formed between the solidified shell 3-2 and the solidified shell 3-2.
-2, which prevents rapid cooling of the solidified shell, resulting in a coarse metallographic structure.

In FIG. 3, when the lower end 10 of the contact limiting plate is located below 20 mm below the bath surface of the molten metal, the solidified shell is pressed against the surface of the casting roll by the static pressure of the molten metal to form an air insulating layer. The solidified shell 3-2 is rapidly cooled by being blocked or the air heat insulating layer becomes thin, and as a result, the solidified shell has a fine metal structure with crystal grains of 50 μm or less.

As described above, the carbon steel slab obtained by the twin-roll continuous casting according to the present invention has a thickness of 0.5 to 6 mm and an average depth of 50 μm or less from the surface to a depth of ４ of the plate thickness. It is characterized by being formed of crystal grains.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present inventors rotated a casting roll having a diameter of 1200 mm and a body length of 800 mm at a peripheral speed of 80 m / min to obtain a molten low carbon steel having a [C] content of 0.04%. Injection was performed to prepare a twin-roll continuous cast slab having a thickness of 3 mm.

At this time, in the example of the present invention, a contact limiting plate is used, the lower end of the contact limiting plate is set to 120 mm below the bath surface, and the distance between the lower end of the contact limiting plate and the surface of the casting roll is set to 0.1 to 1.1.
The casting was maintained at 0 mm. The metal structure of 1/4 from the surface of the cast slab obtained in the present invention was formed of crystal grains of 32 μm on average. Incidentally, the elongation in the L direction of the cast slab obtained in this example of the present invention was 20% and was sufficiently ductile.

As a comparative example, casting was performed without using a contact limiting plate. The other casting conditions are the same as those of the present invention. From the surface of the cast slab obtained in this comparative example, 1/4 of the metal structure was formed of 87 μm average crystal grains. The elongation in the L direction of the slab obtained in this comparative example is 12%, which is inferior to the slab of the present invention in ductility.

[0017]

According to the present invention, with sufficient ductility,
A carbon steel slab with fine crystal grains can be manufactured. Further, in the present invention, since the contact limiting plate is used, no scum is generated on the cast slab, and the solidified shell starts to be formed at a position sufficiently distant from the molten metal bath surface 7.
The influence of the rocking of the molten metal is small, and the wrinkles on the surface of the slab, which usually occur due to the rocking of the bath surface of the molten metal, are greatly reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a relationship between a set position of a contact limiting plate and a size of a crystal grain of a slab.

FIG. 2 is an explanatory view of a normal twin-roll continuous casting.

FIG. 3 is an explanatory view of a twin-roll continuous casting having a contact limiting plate.

[Explanation of symbols]

1-1, 1-2: casting roll, 2: pool, 3-
1,3-2: solidified shell, 4: kiss point, 5: molten metal,
6: cast slab, 7: bath surface of molten metal, 8: rotating direction of casting roll, 9: contact limiting plate, 10: lower end of contact limiting plate, 11: start position of formation of solidified shell, 12 (1)
2 '): Side dam.

Continuation of the front page (56) References JP-A-6-246399 (JP, A) JP-A-6-246398 (JP, A) JP-A-3-193245 (JP, A) JP-A-63-195253 (JP) , A) JP-A-63-119949 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 11/06 330 B22D 11/00

Claims (2)

(57) [Claims] (1) a thickness of 0.5 to 6 mm and a thickness of 1
A carbon steel slab by twin-roll continuous casting, characterized in that crystal grains having a depth of up to / 4 are formed of crystal grains of 50 μm or less. 2. A twin-roll type continuous casting using a contact limiting plate, wherein the lower end of the contact limiting plate is at least 20 mm below the molten metal bath surface and 3/4 of the casting roll radius from the bath surface. , And at the same time, a carbon steel slab is cast while maintaining the distance between the lower end of the contact limiting plate and the surface of the casting roll at 0.1 mm or more and 1 mm or less, twin roll continuous. A method for producing carbon steel slabs by casting.