JPH0417963A - Method for continuously casting steel using direct current magnetic field - Google Patents

Abstract

PURPOSE:To restrain rapid molten steel flow and surface variation in a mold by generating magnetic field toward vertical direction to meniscus at the meniscus corresponding part and parallel magnetic field to the meniscus at below the meniscus in the mold. CONSTITUTION:Two or more coils 3 are set so as to surround the molten steel at the meniscus corresponding part and below the meniscus in the mold, and DC currents are conducted to mutually reverse directions, to generate cusp magnetic field, and at the meniscus corresponding part, electromagnetic force for generating the magnetic field toward the vertical direction to the meniscus, is given and at below the meniscus, the electromagnetic force for generating the magnetic field parallel with the meniscus is given. The magnetic field toward the vertical direction to the meniscus restrains free surface vibration of the molten steel. Further, the magnetic field, which is parallel with the meniscus and intense at outer periphery in the mold and zero at center part, is generated and the molten steel flow can be made to uniformized slow flow. The operation is stabilized and the cast slab having good surface characteristic can be produced.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a continuous casting method for steel, and more specifically, it suppresses rapid fluctuations of molten steel in a mold, suppresses vibrations on the surface of the molten steel, and improves surface quality. This paper relates to a continuous steel casting method using a direct current magnetic field to produce slabs.

As is well known in the art, in the continuous casting method, molten steel is continuously supplied to a mold, a solidified shell is generated within the mold, and the molten steel is continuously drawn out from below the mold to produce slabs. .

In order to facilitate this continuous drawing, powder is introduced into the mold and the mold is moved up and down (hereinafter referred to as oscillation). As a result, regular irregularities, so-called oscillation marks, are formed on the surface of the slab.

However, due to fluctuations in the weight of the tundish or casting speed, or due to the adhesion and peeling off of inclusions from the level control device such as molten metal, the amount of poured molten metal changes rapidly, causing drifting in the mold and rapid fluctuations in the molten metal level. However, the actual situation is that the regular unevenness described above cannot be obtained.

Therefore, in order to prevent the deterioration of the surface quality due to fluctuations in the flow of molten steel, various measures have been taken, such as optimizing the shape of the submerged nozzle, controlling the flow direction of the mold by applying electromagnetic force, or suppressing oscillation vibration by applying electromagnetic force near the meniscus. proposals have been made.

For example, as shown in JP-A-81-199557, a magnetic field is applied perpendicularly to the molten steel in the mold to suppress the flow of molten steel, and as shown in JP-A-81-208550, the above-mentioned system is applied. By applying electromagnetic force in the direction of canceling the rations, we can eliminate ripples on the molten steel surface, smooth the surface level, and improve the surface quality, and apply a DC magnetic field in a direction perpendicular to the surface waves to suppress the surface waves ( Proposals such as Tetsu to Hagane 87, S 1447) have been made.

Problems to be Solved by the Invention However, the above-mentioned technique for suppressing the flow of molten steel in the mold, such as applying a magnetic field in a direction perpendicular to the molten steel in the mold, sufficiently suppresses the flow of molten steel in the mold, and at the same time prevents the flow of molten steel in the meniscus. It is impossible to generate an appropriate flow of molten steel that supplies enough molten steel heat to prevent Deitzkel generation, etc., and deterioration of the surface quality is unavoidable.

In addition, the two ideas for suppressing surface vibrations described below are aimed at suppressing the constantly occurring fluctuations in the melt level by focusing on the self-evident surface resonance phenomenon within the mold. If a large fluctuation in the melt level occurs due to the change, it is not possible to completely stop the reversal wave moving up the short piece, resulting in unevenness on the surface of the slab due to the fluctuation in the melt level.

The present invention aims to fundamentally solve the problems of the conventional methods and provides a continuous casting method capable of producing slabs with excellent surface properties.

Means for Solving the Problems The present invention for solving the problems described above provides a method for continuous casting of steel, in which two or more coils are installed in a part corresponding to the mold meniscus and below it so as to surround the molten steel, A cusp magnetic field is generated by passing direct current in mutually opposite directions, and an electromagnetic force that generates a magnetic field in a direction perpendicular to the meniscus is applied to the part corresponding to the meniscus, and a magnetic field parallel to the meniscus is generated below the meniscus. Its purpose is to impart electromagnetic force.

A coil is installed so that the lower or upper end of the coil is within 150 mm above and below the meniscus, surrounding the portion corresponding to the meniscus, preferably the molten steel, and applying an electromagnetic force that generates a magnetic field in a direction perpendicular to the meniscus. This makes it possible to suppress the free surface vibration of the molten steel in the mold that advances on the meniscus surface.

In particular, if the coil is installed in a range where the bottom end of the coil is 100 mm from the position corresponding to the meniscus, the meniscus will form a vertical magnetic field that is not affected by the coils below, resulting in the most effective braking force. can be granted. This means that the magnetic coil disposed in the upper stage is located at a position that includes the meniscus part of the molten steel, and is located 100 meters below the meniscus part.
It is to be within mm. If the lower end of the coil is 150 mm or more above the meniscus, the direction of the magnetic field at the meniscus will no longer be vertical, and it will be necessary to flow an excessive amount of current to obtain effective braking force. In addition to the upper end being located below the meniscus, there is a problem in that it is not possible to maintain a sufficient distance from the lower coil, making it difficult to effectively damp the upward flow of the short piece, which will be described later.

Paired with this coil, below the mold meniscus, which will be described later,
The optimum position will vary depending on the shape of the immersion nozzle and the immersion depth, but preferably the coil is placed so as to surround the molten steel at a position where the centers of the lower end of the upper coil and the upper end of the lower coil are 50 mm to 250 mm below the meniscus. By installing the coils and passing direct current in opposite directions, a cusp magnetic field is generated between the pair of coils.

This generates a magnetic field that is parallel to the meniscus and strong at the outer periphery of the mold cross section and zero at the center of the cross section in the coil and the cross section where the coil is processed, giving a large braking force to the locally fast reversal flow near the short piece. However, by distributing the flow to the center of the cross section where the braking force is weak, it is possible to create an equalized slow flow.

If the centers of the upper and lower coils are shallower than 50 mm below the meniscus, the distance from applying braking force to reaching the meniscus is short, so in order to obtain a slow flow, it is necessary to apply an excessive braking force, such as a large current. Practical implementation is difficult. On the other hand, 25
In a general operation mode deeper than 0 mm, electromagnetic force is applied from the short piece collision area to the short piece descending area, and it is difficult to make the effective short piece upward flow into an equalized slow flow.

At this time, providing one or more pairs of coils is an effective means for more effectively controlling the short-piece reverse flow.

Effect The present inventors measured the surface flow velocity of molten steel in the mold in order to confirm the above-described effect of suppressing the upward flow of the short pieces.

As a result, by applying horizontal electromagnetic force at an appropriate position, the unsteady initial fluctuations in the molten steel surface flow velocity caused by rapid fluctuations in the stopper are slowed down to 1/4, and the subsequent surface vibrations continue. By applying vertical electromagnetic force at an appropriate position, the vibration that previously lasted for 10 seconds can be reduced to about 3 seconds.
It was confirmed that the time has been shortened by seconds.

As a result, the surface unevenness has been significantly improved, the number of inclusions trapped under the surface of the slab has been reduced to 1/10, and the maintenance-free rate has been significantly increased from less than 1% to a maximum of approximately 30%. Improved. In particular, the magnetic coil installed in the upper stage should be placed at a position that includes the meniscus of molten steel, or from just below the meniscus.
When the distance is within 100+mm, the above-mentioned effect can be more prominently exhibited.

Embodiment FIG. 1 is an overall front view of a mold equipped with a cusp magnetic field generator according to the present invention. In this example, the meniscus portion ±
A coil 3 is attached to surround the mold at a position of 150 mm and 200 mm below the meniscus.

The operating conditions of this example are that stainless steel was continuously cast with a slab size of 1020 mm, a thickness of 250 layers, and a casting speed of 0.6 m/win. Cusp magnetic field generating coil 3
A mold having the ability to generate a central magnetic flux density of 200 to 1500 Gauss in the cross section of the mold was used, and in this example, the highest magnetic flux density of around 1500 Gauss was provided.

Figure 2 shows the amount of subepidermal inclusions produced by this example in comparison with the conventional method.As shown in Figure 0, A is the case where the upper coil is meniscus ±150 mm;
It can be seen that the amount of subepidermal inclusions was significantly improved by applying electromagnetic force.

As a result, the casting hand maintenance rate was reduced, the no-maintenance rate was 10% or more, and the inclusion index was improved to 30%. Further, as shown in FIG. 1, in case B in which the upper coil is provided in the meniscus portion, the maintenance-free rate is 30% and the inclusion index is 16, which is a significant improvement.

Effects of the Invention As detailed above, the present invention suppresses the rapid flow of molten steel within the mold, and also significantly reduces surface fluctuations. As a result, operations have become more stable, it has become possible to produce slabs with excellent surface texture and less unevenness, and the rate of no-maintenance slabs has been significantly improved.

[Brief explanation of drawings]

FIG. 81 is a front view of a mold equipped with an electromagnetic coil based on the present invention, and FIG. 2 is a graph showing the effects of the invention. 1. 110 mold, 2... immersion nozzle, 3a... electromagnetic coil, 4. IIQ tampuy, shoe.

Claims (1)

[Claims] In a method of continuous casting of steel, two or more coils are installed to surround the molten steel at the part corresponding to the meniscus of the mold and below it, and a cusp magnetic field is generated by passing direct current in opposite directions to the part corresponding to the meniscus. Continuous casting of steel using a direct current magnetic field characterized by applying an electromagnetic force that generates a magnetic field in a direction perpendicular to the meniscus, and applying an electromagnetic force that generates a magnetic field parallel to the meniscus below the meniscus. Law.