RU2428274C1 - Method of steel continuous casting - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy. Molten metal is fed into swinging crystalliser to feed mix forming slag well accretion onto crystalliser surface and continuously cast billet is drawn from crystalliser. Crystalliser swings up and down at increased speed in alternating cycles during the entire stay of metal surface element in crystalliser. Crystalliser is swung in transition period by sine law. Crystalliser motion time in transition period equals that of crystalliser up travel with increased speed while relation between crystalliser motion time in transition period and crystalliser down travel with increased speed varies from 1:2 to 1:4.

EFFECT: reduced number of dog's ear defects.

2 cl, 1 ex, 1 tbl

Description

The invention relates to ferrous metallurgy, and more particularly to continuous casting of steel.

The crystallizing shell of a continuously cast billet has a low strength, especially in the meniscus zone. It may burst when pulling the workpiece. This disrupts the crystallization process, causes deterioration of the internal structure of the ingot and defects on its surface. Therefore, to reduce the influence of shell ruptures on the quality of the continuously cast billet, the mold is given a reciprocating motion (rocking).

A known method of continuous casting of steel [1], which includes supplying molten metal to a swinging mold, supplying a slag-forming mixture to the metal meniscus with the formation of a slag skull, drawing a continuously cast billet from the mold, swinging the mold according to a sinusoidal law of motion:

where S is the movement of the mold, mm;

A - swing amplitude of the mold, mm;

ω is the angular frequency, 1 / s;

t is the time, s.

The swing speed of the mold is determined by the equation of motion:

where V is the swing speed of the mold, mm / s;

- производная от перемещения по времени;

- derivative of time travel;

ω is the angular frequency, 1 / s;

A - swing amplitude of the mold, mm;

t is the time, s.

A known method of continuous casting of steel [2], which includes supplying molten metal to a swinging mold, supplying a slag-forming mixture to the metal meniscus with the formation of a slag skull, drawing a continuously cast billet from the mold, swinging the mold according to a non-sinusoidal law, in which the mold moves upward for more than time mold downward movement in one swing cycle. This method more effectively reduces the friction forces acting between the surface of the continuously cast billet and the walls of the mold compared to a method that uses the sinusoidal rocking law of the mold (1), (2).

A known method of continuous casting of steel [3], which includes supplying molten metal to a swinging mold, supplying a slag-forming mixture to the metal meniscus with the formation of a slag skull, drawing a continuously cast billet from the mold and controlling the quality of the billet after rolling. This method is the closest analogue (prototype) of the proposed method.

The disadvantages of these methods include the fact that when they are used on the surface of a continuously cast billet, transverse cracks can form along the swing folds and non-metallic inclusions polluting the fold area, leading to discontinuity and a decrease in the ductility of the metal in this zone. During rolling of continuously cast slabs, transverse cracks along the rocking folds of the mold and accumulations of non-metallic inclusions are transformed into “captivity” defects on the sheet surface, which negatively affect the service properties of the finished products and lead to a decrease in product quality. Also, in connection with the technologically necessary change in the speed of drawing the workpiece during casting, the question arises of bringing the swing parameters of the mold in accordance with it, so there is a need to reduce inertial loads in the swing mechanism of the mold and its drive.

The problem to which the invention is directed is to improve the surface quality of a continuously cast billet due to a “defect” defect by increasing the thickness of the slag film between the surface of the continuously cast billet and the walls of the mold, reducing thermal cycling in the mold, reducing metal contamination by exogenous non-metallic inclusions, and reducing inertial loads in the swing mechanism of the mold and its drive.

The technical result of the invention is to improve the surface quality of the slab and sheet, reducing the sorting of finished products by the defect of the "captivity" after rolling.

This problem is solved due to the fact that in the method of continuous casting of steel, comprising supplying molten metal to a swinging mold, supplying a slag-forming mixture to the metal meniscus with the formation of a slag skull, drawing a continuously cast billet from the mold and controlling the quality of the workpiece after rolling, according to the invention, the mold is pumped with alternating cycles with an increased speed of the mold up and / or with an increased speed of the mold down for a residence time of the metal surface member in the mold, and the mold oscillation during transient carried out sinusoidally.

In addition, the time of motion of the mold during the transition mode is equal to the time of motion of the mold with increased speed up, and the ratio of the time of motion of the mold during transition to the time of motion of the mold with increased speed down is in the range from 1: 2 to 1: 4.

The residence time of the element of the metal surface in the mold t is determined by the formula:

where h is the height of the metal level in the mold, m;

V _p is the speed of drawing (casting), m / min.

Non-metallic inclusions in the area of rocking folds during rolling of continuously cast slabs are transformed into surface defects of the “captive” sheet, which negatively affect the service properties of the finished products and lead to product sorting. Therefore, it is necessary to take measures to prevent the ingress of non-metallic inclusions into the melt. During the crystallizer moving upward at an increased speed, the meniscus crust rises above the level of molten steel in the mold, which helps to reduce metal contamination by exogenous non-metallic inclusions.

Friction between the shell of the continuously cast billet and the walls of the mold depends on the flow rate of the slag-forming mixture (SCO). When the mold is swung with an increased downward speed, the SCO is better drawn between the walls of the mold and the shell of the continuously cast billet, the SCO consumption increases, as a result of which friction between the shell of the continuously cast billet and the walls of the mold decreases.

The swing of the mold is carried out with alternating cycles with an increased speed of the mold up and / or with an increased speed of the mold down during the residence time of the metal surface element in the mold.

With a greater share of participation in the formation of the “captivity” defect of rolled non-metallic inclusions, rocking of the mold with a large time with an increased speed of upward movement is used. With a greater share in the formation of the “captivity” defect of rolled cracks, mold swinging is used with a long time with an increased downward speed.

The swing of the mold during the transition mode, which acts between the movements of the mold cycles with increased speed up and / or down, is carried out according to a sinusoidal law, which allows to reduce inertial loads in the swing mechanism of the mold and its drive.

The proposed method of continuous casting of steel is as follows.

During continuous casting, metal is fed into a swinging mold, a slag-forming mixture is fed to the metal meniscus with the formation of a slag skull and a continuously cast billet is pulled out of the mold, the mold is rocked with alternating cycles with an increased mold speed up and / or with an increased mold down motion speed the residence time of the metal surface element in the mold, the swing of the mold during the transition mode according to a sinusoidal law and control the quality of the workpiece. The residence time of the metal surface element in the mold t is determined by the formula (3). And the time the mold moves up and / or down is directly dependent on the fraction, respectively: rolled non-metallic inclusions and / or rolled cracks involved in the formation of the “captivity” defect. With a greater share of participation in the formation of the “captivity” defect of rolled non-metallic inclusions, rocking of the mold with a large time with an increased speed of upward movement is used. With a greater share in the formation of the “captivity” defect of rolled cracks, mold swinging is used with a long time with an increased downward speed.

Example.

A pilot trial of the developed method for continuous casting of steel was carried out. To do this, 17G1SU steel was fed into a swinging mold with a length of 900 mm and a metal level in it h = 750 mm, a slag-forming mixture was fed to the metal meniscus with the formation of a slag skull, and a continuously cast billet was pulled from the mold at a speed of 1.0 m / min. The residence time of the metal surface element in the mold was 0.75 minutes, and the mold was rocked with alternating cycles with an increased rate of mold motion up and with an increased velocity of the mold down during the residence time of the metal surface element in the mold. The swing of the mold was carried out according to a non-sinusoidal law with a swing amplitude of A = 4 mm, a casting speed of 1.0 m / min and a frequency of 1.5 Hz. In this case, the efforts of pulling the workpiece from the mold were measured and the quality of the rolled products was monitored.

The obtained results were compared with the prototype, where the mold was swinging according to a non-sinusoidal law with a swing amplitude of A = 4 mm, a casting speed of 1.0 m / min and a frequency of 1.5 Hz, and where the effort to pull the workpiece from the mold was 31.5 kN, flow rate The SCO is 0.8 kg / t, and the sorting of rolled products according to the “captivity” defect is 18.6%.

The results of the application of the proposed method in comparison with the prototype are shown in the table, which shows that the best results were obtained when the mold was moving during the transition mode, equal to the mold moving time with increased speed up, and its ratio to the mold moving time with increased speed down as 1: 2, 1: 3, 1: 4.

This invention makes it possible to improve the surface quality of a continuously cast billet due to a “defect” defect by increasing the thickness of the slag film between the surface of the continuously cast billet and the walls of the mold, reducing thermal cycling in the mold, reducing metal contamination by exogenous non-metallic inclusions, and also reducing inertial loads in the swing mechanism and its drive.

List of sources used

1. Niskovsky V.M., Karlinsky S.E., Berenov A.D. Machines for continuous casting of slab billets. - M.: Metallurgy, 1991, p. 55-69.

2. Suzuki M., Mitsukami X., Kitagawa T., Kawakami K., Uchida Sh., Komatsu I. Development of a new mold swinging mode for high-speed continuous casting of slabs. All-Union Translation Center (VTsP) No. of transfer Ya-13700 06/18/1992.

3. RF patent for the invention No. 2378083 C1 "Method for continuous casting of steel" 10.01.2010.

Claims (2)

1. A method of continuous casting of steel, comprising supplying molten metal to a swinging mold, supplying a slag-forming mixture to the metal meniscus with the formation of a slag skull, drawing a continuously cast billet out of the mold and controlling the quality of the workpiece after rolling, characterized in that the mold is swung with alternating cycles with increased the speed of the mold up and / or with an increased speed of the mold down during the residence time of the element on top metal in the mold, and the swing of the mold during the transition mode is carried out according to a sinusoidal law. 2. The method according to claim 1, characterized in that the mold motion time during the transition mode is equal to the mold motion time with increased speed up, and the ratio of the mold motion time during the transition mode to the mold motion time with increased speed down is in the range from 1 : 2 to 1: 4.