JP3104000B2 - Light reduction method in continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prevents the segregation of impurities such as sulfur, phosphorus, manganese and the like found in the center of the thickness of a continuous cast slab, for example, in the case of steel slab, and obtains a homogeneous metal. The present invention relates to a light reduction method in continuous casting.

[0002]

2. Description of the Related Art In recent years, requirements for material properties of marine structures, storage tanks, steel pipes for oil and gas transportation, high-strength wires, and the like have become increasingly severe, and providing a homogeneous steel material has become an important issue. I have.

[0003] Originally, steel materials should be homogeneous in cross section, but steel generally contains impurity elements such as sulfur, phosphorus and manganese, which segregate during the casting process and partially concentrate. The steel becomes brittle. Especially in recent years,
Although the continuous casting method is widely used for the purpose of improving productivity and yield, saving energy, and the like, remarkable component segregation is usually observed at the center of the thickness of a slab obtained by continuous casting. This segregation of components significantly impairs the homogeneity of the final product, and causes serious defects such as cracks caused by stress acting on the steel during the use process of the product and the wire drawing process of the wire rod. .

[0004] Such component segregation is caused by the residual molten steel flowing due to the solidification shrinkage force or the like in the final stage of solidification, washing out the concentrated molten steel near the solid-liquid interface, and the residual molten steel progressively becoming concentrated. Therefore, in order to prevent component segregation, it is important to remove the cause of the flow of the residual molten steel.

The causes of such molten steel flow include, besides the flow caused by solidification shrinkage, the flow caused by slab bulging between rolls, and the misalignment of rolls. The most significant of these is solidification shrinkage. In order to prevent segregation, it is necessary to reduce the slab by an amount that compensates for this.

[0006] Attempts to improve segregation by rolling down a slab have hitherto been made.
There is known a method in which the slab is lowered at a constant rate equal to or more than an amount for compensating for solidification shrinkage during the time when the temperature of the slab central part reaches the liquidus temperature to the solidus temperature.

[0007]

However, in the conventional light rolling method, the slab is reduced while the slab is being drawn, but the casting speed becomes 0 during casting, and the slab is pulled out. When stopped, no reduction was performed on the slab and no compensation for solidification shrinkage was made, so that segregation could not be improved.

[0008]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a method for continuously casting a molten metal, in which the casting speed is set to 0 and the slab drawing is stopped in the light reduction method in continuous casting of molten metal. The roll at the slab position where the elapsed time from the meniscus is the time at which the solid phase ratio is 0.1 to 0.3 is set as the roll reduction position control start position, and the elapsed time from the meniscus is the solid phase ratio. The roll at the slab position where the time becomes 0.5 to 0.7 is defined as the roll reduction position control end position, and the reduction cylinder is used so that the roll existing between the rolls can secure the reduction speed required for solidification shrinkage compensation. This is a light pressure reduction method in continuous casting that controls the oil pressure and the roll interval. Further, the required rolling speed at the time of stopping the drawing of the slab is preferably set to α times (α> 1) 0.5 to 2.5 mm / min, which is the rolling speed required at the time of drawing the slab.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a light reduction method for compensating for solidification shrinkage when drawing of a slab is stopped in a continuous casting machine.

FIG. 1 is a view showing an example of a continuous casting machine for carrying out the present invention. The slab 3 is normally continuously withdrawn from the meniscus position, and roll no. A light reduction is performed between 30 and 50. When the casting speed fluctuates or when the slab drawing is stopped, the roll No. The roll interval in the necessary roll range among 20 to 50 is controlled to reduce the pressure.

Since the solidification state in which solidification shrinkage compensation is required is considered to be the same regardless of the presence or absence of slab drawing, the required rolling range is the slab drawing described in Japanese Patent Application No. 60-171315. Similarly to the appropriate rolling range at the time, the roll position where the solid phase ratio is 0.1 to 0.3 is the roll interval control start position, and the roll position where the solid phase ratio is 0.5 to 0.7 is the roll interval control. End position. The solid fraction can be expressed as a function of the time elapsed from the meniscus. The elapsed time from the meniscus can be expressed by Expression 1, and the solid fraction is expressed by Expression 2, for example.

[0012]

(Equation 1) t _j: time elapsed from the meniscus in the j-th roll pressing position L _i: up to its role position, length t _s casting speed is V _i: up to its role position, time slab withdrawal is stopped

[0013]

(Equation 2) f _s : solid fraction a _n : constant t: elapsed time from meniscus

FIG. 2 is a view showing an example of a rolling roll for carrying out the present invention. In the case of the continuous casting machine shown in FIG. It corresponds to a 20-50 reduction roll. The pressing cylinder 2 is a pressing cylinder capable of detecting a position. The roll interval is obtained from the position detection value of the rolling cylinder 2 and the hydraulic pressure control is performed using the roll interval value to perform the roll interval control for realizing the required reduction amount.

The required rolling speed is obtained as a function of the time elapsed from the meniscus as shown in FIG. What is shown by the dotted line in the figure is the required rolling speed during drawing of the slab,
It is set so that an appropriate value of the average reduction speed between the solid phase ratio of 0.1 to 0.3 and the solid phase ratio of 0.5 to 0.7 is realized.
The appropriate average reduction speed is 0.5 to 2.5 m as shown in FIG.
m / min. If it is larger than this range, segregation worsens due to over-pressure, and if it is smaller than this range, segregation worsens due to insufficient rolling.

When the slab drawing is stopped, it is necessary to compensate not only for the solidification shrinkage immediately below the rolls but also for the solidification shrinkage between the rolls and to reduce the bulging amount. It is necessary, and this can be expressed by Expression 3, and is a value indicated by a solid line in FIG.

[0017]

DR / dt = α × f (t) dR / dt: Appropriate rolling speed at stop of drawing slab α: Correction coefficient (α> 1) f (t): Proper rolling speed at drawing of slab t : Elapsed time from meniscus

When the casting speed is 0 m / min during casting and slab drawing is stopped, the rolling roll in the rolling range is changed by changing the hydraulic pressure of the hydraulic cylinder of the rolling roll,
By controlling the roll interval so as to realize the required rolling speed, the solidification shrinkage compensation at the time of stopping the drawing of the slab becomes possible, and the segregation can be improved.

FIG. 5 shows the segregation state of the conventional light reduction method and the light reduction method according to the present invention when the casting speed becomes zero. The dotted line is the conventional light reduction method, and the solid line is the present invention. According to the present invention, a good segregation level can be realized over the entire length.

[0020]

According to the present invention, solidification shrinkage can be compensated for even when slab drawing is stopped, and segregation can be improved. By combining with the conventional light reduction technology, segregation can be improved over the entire length of the slab.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a continuous caster for implementing the present invention.

FIG. 2 is a diagram showing an example of a slab reduction roll for implementing the present invention.

FIG. 3 is a diagram showing a reduction amount required in the present invention.

FIG. 4 is a diagram showing an appropriate average rolling speed in a conventional rolling method.

FIG. 5 is a diagram showing the effect of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reduction roll 2 Reduction cylinder 3 Cast piece 4 Roll stand 5 Mold

Continuation of the front page (56) References JP-A-5-50201 (JP, A) JP-A-4-33757 (JP, A) JP-A-5-15956 (JP, A) JP-A-5-212517 (JP) JP-A-58-6759 (JP, A) JP-A-63-183762 (JP, A) JP-A-4-22549 (JP, A) JP-A-6-190521 (JP, A) JP-A-4-313454 (JP, A) JP-A-4-313453 (JP, A) JP-A-4-279264 (JP, A) JP-A-62-275556 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/20 B22D 11/128 350

Claims (2)

(57) [Claims] In a light reduction method in continuous casting of molten metal for continuously drawing a slab, the casting speed is reduced to 0 during casting.
When the slab drawing is stopped, the roll at the slab position where the elapsed time from the meniscus is the time at which the solid phase ratio is 0.1 to 0.3 is the roll reduction position control start position, The roll at the slab position where the elapsed time from the meniscus is 0.5 to 0.7 in terms of the solid phase ratio is set as the roll reduction position control end position, and the roll between the rolls is required for solidification shrinkage compensation A light reduction method in continuous casting that controls the hydraulic pressure of the reduction cylinder and controls the roll interval so that a proper reduction speed can be secured. 2. The required rolling speed at the time of stopping the drawing of the slab is 0.5 to 2.5 m, which is the rolling speed required at the time of drawing the slab.
2. The light reduction method in continuous casting according to claim 1, wherein the value is α times m / min (α> 1).