JPH05277657A - Method for controlling inclined angle of columnar crystal structure in cast strip in twin roll casting - Google Patents

Abstract

(57) [Summary] [Purpose] In twin roll casting for producing thin slabs,
Provided is a method for controlling the tilt angle of a thin slab columnar crystal structure for controlling the tilt angle of the columnar crystal structure of a solidified shell. [Structure] A contact limiting plate 4 charged in a molten metal pool 3 formed between two rolls 1a and 1b is moved up and down, and a distance from a solidification start point 6 to a roll kiss point 7 and a rotation speed of the roll are set. By controlling the formation rate and cooling rate of the solidified shell 8 to control the inclination angle of the columnar crystal structure of the solidified shell formed to a desired angle. [Effect] The tilt angle of the columnar crystal structure of the solidified shell can be controlled to a desired angle, and if this is applied to electrical steel sheets, the material for high-grade non-oriented electrical steel sheets with high magnetic properties (high magnetic flux density, low iron loss) can be obtained. It can be manufactured stably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a tilt angle of a columnar crystal structure of a thin cast piece for controlling a tilt angle of a columnar crystal structure of a solidified shell to be formed in twin roll casting for manufacturing a thin cast piece.

[0002]

2. Description of the Related Art A twin-roll type continuous casting method in which molten steel is poured between two rolls rotating inward and a thin metal plate is cast is known as a Bessemer method.

In this method, two rolls are arranged at appropriate intervals, and when the molten metal is poured from above and rotated inside each other, the poured molten metal comes into contact with the rolls to remove heat, As a result, a solidified shell is formed on the roll surface,
As the roll rotates, the two solidified shells are joined together, and further pressed to form a slab of a predetermined thickness, which is then delivered below the roll to produce a thin plate slab.

In this case, the solidified shell begins to solidify at the point where the molten metal comes into contact with the roll, continues to grow, and becomes a solidified shell having a predetermined thickness at the roll kiss point. Since it becomes a slab, it is necessary to accurately control the distance from the solidification start point to the roll kiss point in order to maintain the dimensional accuracy and surface quality of the slab to be manufactured.

By the way, it is preferable that the solidification structure of the slab that grows at the same time grows perpendicularly to the surface of the solidification shell as a columnar crystal structure (hereinafter referred to as dendrite) shown in FIG. 2. For example, this is the plate surface. In the case of the cast slab 9 having the dendrites 10 in which the <100> orientation is aligned in the direction perpendicular to, it is possible to manufacture a non-oriented electrical steel sheet having excellent magnetic properties.

[0006]

As these conventional techniques, for example, there is a technique of a twin roll type casting and rolling mill disclosed in Japanese Patent Publication No. 62-58811 and its control method.

In this technique, a molten steel pool formed by two rolls is provided with a limiting plate for adjusting the contact area between the rolls and the molten steel, that is, a contact limiting plate.
Twin roll cast rolling that sets the opening of the contact limiting plate that slides on the roll surface to a desired value to control the contact area between the molten steel and the roll in the pool and controls the thickness of the solidified shell that is formed. It is the control method of the machine.

In this case, the formed thickness of the solidified shell is approximately proportional to the arc length from the solidification start point where the tip of the contact limiting plate contacts the roll to the roll kiss point, and the cooling effect of the roll, when the roll rotation speed is constant. Determined by Noh. Therefore, the longer the arc length to the roll kiss point and the larger the cooling ability of the roll, the faster the solidified shell grows.

Therefore, by sliding the contact limiting plate up and down along the roll surface, the arc length from the solidification start point to the roll kiss point can be changed and the thickness of the solidified shell formed can be controlled.

However, this technique is extremely effective for controlling the plate thickness of the slab and improving the surface quality, but the dendrite is usually inclined by 10 to 20 degrees with respect to the casting direction, which is industrial It is difficult to obtain a dendrite perpendicular to the plate surface of 10 degrees or less with a large-scale casting machine of a production scale.

The growth of dendrites is SRNC-90 "INTERNAT
IONAL CONFERENCE ON NEW SMELTINGAND NEAR NET SHAPE
CASTING TECHNOLOGIES FOR STEEL "14-19 Oct, 1990 R
IST, Pohang / Korea (THE KOREAN INSTITUTE OF METALS
& THE INSTITUTE OF METALS, UK)
Further, as shown in FIG. 2, in the case of twin roll thin plate casting, it is known that the inclination angle θ is largely inclined to the casting direction at 10 to 20 degrees.

Further, in Japanese Patent Application No. 61-84091, in twin-roll casting of non-oriented electrical steel, a slab having dendrites with <100> orientations aligned in a direction substantially perpendicular to the plate surface is produced. A technology has been filed that enables the production of non-oriented electrical steel sheets with excellent magnetic properties.However, since dendrites are not completely perpendicular to the plate surface but are inclined in the casting direction, they achieve ideal magnetic properties. I couldn't do it.

In view of the above-mentioned problems, the present invention controls a tilt angle of a columnar crystal structure of a solidified shell to be formed in twin roll type casting for producing a thin slab to obtain a non-oriented electrical steel sheet having excellent magnetic properties. A method for controlling a tilt angle of a columnar crystal structure of a thin cast slab is provided.

[0014]

According to the present invention, a thin cast piece is cast by inserting a contact limiting plate for fixing the solidification start point of the molten metal into a molten metal pool formed between two rolls. In twin roll casting, the contact limiting plate is moved up and down to change the distance from the solidification start point to the roll kiss point and the rotation speed of the roll, and the formation speed and cooling speed of the solidification shell are controlled to form A method for controlling the tilt angle of a thin cast columnar crystal structure in twin roll casting, comprising controlling the tilt angle of the columnar crystal structure of the solidified shell to a desired angle.

[0015]

FIG. 1 is a side view showing a situation in which a thin slab is cast in twin roll casting. Reference numerals 1a and 1b denote a pair of casting rolls. Side weirs 2 are attached to opposite side surfaces of the upper part of the rolls to form a molten steel pool 3 between the rolls. A contact limiting plate 4 is provided on the roll surface of the pool 3
Is loaded from above.

The molten metal poured from the pouring nozzle 5 into the molten metal pool 3 starts to solidify because the surface of the molten metal is cooled from the point of contact with the solidification starting point 6 in contact with the rolls 1a and 1b at the tip of the contact limiting plate 4. The solidified shells 8 formed on both roll surfaces at the roll kiss points 7 are integrated and drawn downward to form a cast piece 9.

The thickness of the solidified shell 8 formed in this case is substantially proportional to the arc length from the solidification start point 6 to the roll kiss point 7,
Moreover, the larger the cooling capacity of the roll, the faster the solidified shell grows.

It is also described in the above-mentioned document that the inclination angle of the dendrite formed in the thin slab cast by the twin roll method has a great influence on the rotation speed of the roll. That is, if the arc length from the solidification start point to the roll kiss point is increased and the solidification shell is rapidly cooled by the roll, it is necessary to increase the roll rotation speed in producing a slab of the same plate thickness, and the dendrite is produced. The inclination angle of becomes large. On the contrary, if the arc length is shortened and the cooling capacity of the roll is reduced, the roll rotation speed can be reduced, so that the dendrite inclination angle becomes smaller.

According to the present invention, when casting a slab having the same plate thickness with the same casting machine, the contact limiting plate is charged in the molten metal pool,
By moving this up and down to change the distance from the solidification start point to the roll kiss point, and by changing the rotation speed of the roll to control the growth rate of the solidification shell, the inclination angle of the dendrite to be formed in the casting direction is changed. The angle is controlled to a desired angle.

[0020]

EXAMPLES Examples of the present invention will be described below.

In this embodiment, the diameter shown in FIG. 1 is 400 mm.
Copper roll, molten steel / roll contact length 150mm,
Steel type 1% Si steel, a thin plate slab with a plate thickness of 2 mm was manufactured.
In this case, the immersion depth of the contact limiting plate was changed to 0 to 120 mm, the casting speed was changed to 30 m to 7 / min, casting was performed, and the columnar crystal structure inclination angle in each case was measured. The results are shown in Table 1.

[0022]

[Table 1]

As described above, the contact limiting plate is charged into the molten steel pool, the distance from the solidification start point to the roll kiss point is changed, and the rotation speed of the roll is changed to control the growth rate of the solidified shell. By doing so, it is possible to cast a slab having the target dendrite inclination and plate thickness at low speed, and especially when the immersion depth of the contact limiting plate is 120 mm and the casting speed is 7 m / min, the dendrite inclination is about 3 degrees. , A tilt angle close to vertical was obtained.

[0024]

As described above, the method for controlling the dendrite tilt angle of the present invention changes the distance from the solidification start point of the contact limiting plate to the roll kiss point and the rotation speed of the roll to form the solidification shell and the cooling speed. To control the tilt angle of the columnar crystal structure to a desired angle. For example, when this is applied to the production of electromagnetic steel sheets, the <100> orientation is close to the plate surface, and the dendrites are formed over the entire plate thickness. Therefore, it is possible to stably manufacture a high-grade non-oriented electrical steel sheet having high magnetic properties (high magnetic flux density and low iron loss).

[Brief description of drawings]

FIG. 1 is a side view showing a situation in which a thin slab is cast in twin roll casting.

FIG. 2 is a schematic diagram illustrating a dendrite formation state.

[Explanation of symbols]

 1a, 1b Roll for casting 2 Side weir 3 Hot water pool 4 Contact limit plate 5 Injection nozzle 6 Solidification start point 7 Roll kiss point 8 Solidification shell 9 Cast slab 10 Dendrite

Claims (1)

[Claims] 1. In twin roll casting in which a contact restriction plate for fixing the solidification start point of the molten metal is inserted into a molten metal pool formed between two rolls to cast a thin slab, the contact restriction is applied. The tilt angle of the columnar crystal structure of the solidified shell formed by moving the plate up and down to change the distance from the solidification start point to the roll kiss point and the rotation speed of the roll to control the solidification shell formation rate and the cooling rate. Is controlled to a desired angle. A method for controlling the tilt angle of a thin slab columnar crystal structure in twin roll casting.