Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1996-02-23
1997-08-19
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164502, B22D 2702
Patent
active
056578164
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a continuous casting method wherein a direct current magnetic field is applied to the direction of thickness of the mold over the whole width direction to make the molten steel stream uniform, and particularly to a continuous casting method wherein the meniscus flow velocity within the mold is regulated to a specified range.
2. Background Art
It is known that, in continuous casting, the flow of a molten steel within a mold greatly influences the quality of cast slabs and the operation. Specifically, the flow of a molten steel stream delivered through a nozzle brings slag inclusions, included in the molten steel, into a deep portion of a strand pool. The deeper the portion into which the inclusions are brought, the easier the trapping of the inclusions in a solidified shell and, hence, the higher the possibility of occurrence of defects in a cast slab. For this reason, the depth of the entry of a descending stream should be preferably as small as possible. On the other hand, regarding the surface of a molten steel, when the meniscus flow velocity is high as is observed in high-speed casting, entrainment of a powder present on the surface of the molten steel in the molten steel or an increase in a variation in molten steel surface level occurs. When the meniscus flow velocity is low, as is observed in low-speed casting, a deckel is formed on the surface of the molten steel, hindering the operation. Further, in this case, inclusions or Ar bubbles are trapped in solidified shell to deteriorate the quality of the cast slab in its portion very near the surface thereof. For this reason, the meniscus flow velocity should be kept on a constant level. Since it is difficult to attain such a flow pattern through the regulation of the nozzle shape and the nozzle depth from the molten steel surface, several methods for regulating the flow of a molten steel within a mold by taking advantage of a direct current magnetic field have been proposed in the art.
Japanese Examined Patent Publication (Kokoku) No. 2-20349 discloses a method Wherein the flow of a molten steel within a mold is regulated using a direct current magnetic field in this method, a direct current magnetic field is allowed to act on a part of a main passage of a molten steel stream delivered through a submerged nozzle to decelerate the main stream of the molten steel, thereby preventing the entry of a descending stream into a deep portion of a strand pool. At the same time, the main stream is divided into small screams to cause agitation of the molten steel within the pool. In this method, however, since a direct current magnetic field is allowed to act on a part of the width of the mold, a stream delivered through the nozzle, in some cases, bypasses a brake band (a magnetic field band). That is, a stream directed from a place, where the brake is weak, toward the lower part of the pool occurs. This brings inclusions into a deep portion of the pool. Further, in this case, since this phenomenon is not stable, the flow of the molten steel within the mold becomes unstable, resulting in unstable agitation at the upper part of the pool. For this reason, the above method could not improve the quality of the cast slab.
Japanese Unexamined Patent Publication (Kokai) No. 2-284750 discloses a method wherein a direct current magnetic field is applied to the whole region in the width direction of the mold. According to this method, although a stream below the brake band can be brought into plug flow, the direct current magnetic field is applied to a place where braking is applied. Further, the regulation of the meniscus flow velocity is carried out by applying a direct current magnetic field to the whole mold or alternatively by applying a direct current magnetic field in a two-stage manner. A method wherein a direct current magnetic field is applied to a portion below the nozzle hole is also disclosed therein. As described below, however, the meniscus flow velocity is influenced greatly by the angle of mo
REFERENCES:
patent: 5381857 (1995-01-01), Tozawa et al.
Harada Hiroshi
Ishii Takanobu
Takeuchi Eiichi
Toh Takehiko
Lin Kuang Y.
Nippon Steel Corporation
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