JPH08117938A - Method for pouring molten steel in continuous casting of thin slab - Google Patents

Abstract

PURPOSE: To provide a method for pouring molten steel which prevents the adhesion of the base metal in a flat nozzle and the surface defects of a thin slab by preventing the drift of the molten steel which exists in the flat nozzle and is discharged from the flat nozzle in continuous casting of the thin slab. CONSTITUTION: A sliding plate 6 of a sliding nozzle 3 for controlling the supply rate of the molten steel from a molten steel supply vessel to the flat nozzle 5 is slid perpendicularly to the long side direction of the flat nozzle 1 in the method for continuous casting of the thin slab which pours the molten steel by the flat nozzle 5. As a result, the interruption of casting is entirely obviated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in a continuous casting method for thin slabs, prevents uneven flow of molten steel discharged in the flat nozzle and from the flat nozzle to prevent metal adhesion in the nozzle and surface defects of the slab. The present invention relates to a method for pouring molten steel.

[0002]

2. Description of the Related Art In injecting molten steel into a mold in a conventional continuous casting machine, a molten steel supply container, for example, molten steel from a tundish, uses a cylindrical immersion nozzle because the thickness of the casting mold is large depending on the thickness of the cast piece. As a control device for the injection flow rate, the sliding nozzle (hereinafter referred to as SN) has high flow rate control accuracy and high reliability of drive hardware.
The mainstream is to use. In this case, the molten steel in the immersion nozzle may flow out in an unfilled state depending on the opening degree of SN, but since it has a large mold thickness, it has little effect on the slab.

On the other hand, in a thin wall continuous casting machine in which the wall surfaces of the mold are parallel to each other, the molten steel is injected by a flat nozzle having a size corresponding to the mold thickness and the production amount, as disclosed in JP-A-4-37446. in use. The amount of molten steel supplied to the flat nozzle is controlled by SN provided between the molten steel supply container and the flat nozzle. In a flat nozzle, it is extremely important to fill molten steel in a flat nozzle and let it flow out, in order to produce a good slab, and especially when a wide nozzle is used, its effect is remarkable. Appearing, as the width becomes wider, the possibility that molten steel flows unfilled in the nozzle or flows out while drifting increases.

[0004]

The present inventors have studied the sliding direction of the SN sliding plate for controlling the injection flow rate in order to solve the uneven flow in the flat nozzle and obtain a uniform discharge flow. That is, it is important in the casting of thin cast pieces to let the molten steel flow out uniformly and in a filled state from the nozzle outlet, and if a non-filled region where the molten steel flow is poor occurs partially, the nozzle refractory material The adhesion and solidification of the metal into the steel occurs, and the molten steel flow rate required for casting cannot be maintained, resulting in a decrease in production amount and a decrease in nozzle life.

Further, if the discharge flow velocity is uneven in the width direction of the nozzle, solidified shell attack occurs at a portion where the discharge flow velocity is high, causing vertical cracking of the slab due to local solidification delay of the shell. The present invention prevents uneven flow in the flat nozzle and reduces the life of the nozzle due to adhesion of metal in the nozzle.
Also provided is a method for preventing vertical cracking of a slab due to solidified shell attack that occurs due to non-uniformity of nozzle discharge flow.

[0006]

Means for Solving the Problems The present invention is to solve the above problems, and the gist thereof is to provide a molten steel supply in a continuous casting method of a thin slab in which molten steel is injected into a mold by a flat nozzle. A method for injecting molten steel in continuous casting of thin slabs, characterized in that a sliding plate of a sliding nozzle that controls the amount of molten steel supplied from the container to the flat nozzle is slid at a right angle to the long side direction of the flat nozzle.

[0007]

The operation of the present invention will be described below. To investigate the influence of the sliding direction of SN on the nozzle discharge flow velocity, 1
A model experiment of a scale of 1 was performed. The upper nozzle, SN, and flat nozzle were made of acrylic, and the flow rate was measured with a Pitot tube.

Flat nozzle widths of 400 mm and 600 m
50% of SN opening by SN sliding plate for m
The discharge flow velocity was measured by fixing the nozzle to the nozzle, and the 400 mm wide nozzle was slidable in Fig. 3 (a) when the sliding direction of the SN sliding plate was parallel to the long side of the flat nozzle. The case where the directions are right angles is shown. Also, 600
Similarly, for the mm width nozzle, the case of parallel to FIG. 4A and the case of right angle to FIG. 4B are shown.

It is understood from FIGS. 3 and 4 that the sliding direction of the SN sliding plate has a great influence on the discharge flow velocity distribution of the nozzle in any case. For example, in the case of a 600 mm wide nozzle, when the sliding direction of the SN sliding plate is parallel to the long side direction of the flat nozzle, the discharge flow is affected by the SN opening, and the maximum discharge flow velocity is 1.5 times the average flow velocity. However, when the sliding direction is at right angles to the long side direction of the flat nozzle, it is not affected by the opening of the SN and the maximum discharge flow velocity is 1.1 times the average flow velocity and the discharge flow is equalized. ing. Therefore, the equalization of the discharge flow rate from the flat nozzle is
This can be achieved by making the sliding direction of the sliding plate perpendicular to the long side direction of the flat nozzle.

[0010]

FIG. 1 shows an example in which the present invention is applied to an actual machine, and FIG. 2 shows a comparative example. FIG. 1 relates to the present invention, where the sliding direction of the SN sliding plate is perpendicular to the long side direction of the flat nozzle, and FIG. 2 is the sliding direction of the SN sliding plate parallel to the long side direction of the flat nozzle. It is a comparative example in such a case. Supply of molten steel to the mold is a tundish (molten steel supply container)
The molten steel No. 1 is injected through the upper nozzle 2, the sliding nozzle 3, the lower nozzle 4, and the flat nozzle 5, and the molten steel flow rate is controlled by the sliding plate 6.

As an example of the present invention, a continuous casting test was conducted on a medium carbon steel having a high rate of vertical cracking of the slab, and the effect on the operation of the SN sliding plate in the sliding direction and the quality of the slab. Were compared. Casting conditions Mold width: 1300 m, mold thickness: 75 mm Mold speed: 5-10 m / min Injection nozzle: Flat nozzle Discharge port width 600 mm, discharge port thickness 10 mm: Flat nozzle is located in the center of the mold SN: Under casting conditions with an inner diameter of 80 mm or more Table 1 shows the results obtained by casting thin slabs with a twin-belt continuous casting machine and examining the quality of the slabs by operating conditions and visual observation.

[0012]

[Table 1]

By sliding the SN sliding plate at right angles to the long side direction of the flat nozzle, it is possible to prevent the metal from adhering to the inner wall of the nozzle, prevent the set casting speed from decreasing, and never interrupt the casting. there were. In the case of the comparative example in which the SN sliding plate was slid in the direction parallel to the long side of the flat nozzle, vertical cracking of the slab often occurred at the position corresponding to the nozzle discharge port and the side where the SN was open. However, the incidence of vertical cracks could be greatly reduced by sliding in the perpendicular direction in the present invention.

[0014]

According to the present invention, by equalizing the discharge flow from the flat nozzle, it is possible to prevent the adherence and solidification of the metal on the inner wall of the nozzle, ensuring the productivity and preventing the shortening of the nozzle life.
It also enables vertical crack prevention of cast slab.

[Brief description of drawings]

FIG. 1 is a diagram showing a sliding direction of an SN sliding plate according to the present invention.

FIG. 2 is a diagram showing a sliding direction of an SN sliding plate in a comparative example.

FIG. 3 is a diagram showing a flow velocity distribution state according to a sliding direction of an SN sliding plate.

FIG. 4 is a diagram showing a flow velocity distribution state according to a sliding direction of an SN sliding plate.

[Explanation of symbols]

 1 Tundish 2 Upper nozzle 3 Sliding nozzle 4 Lower nozzle 5 Flat nozzle 6 Sliding plate

Claims (1)

[Claims] 1. In a continuous casting method of thin slabs for injecting molten steel into a mold by a flat nozzle, a sliding plate of a sliding nozzle for controlling a molten steel supply amount from a molten steel supply container to the flat nozzle is provided with a flat nozzle long side. A method for pouring molten steel in continuous casting of thin slabs, characterized by sliding at right angles to the direction.