Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1999-08-09
2002-09-03
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S468000
Reexamination Certificate
active
06443219
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
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REFERENCE TO MICROFICHE APPENDIX
Not Applicable
1. Field of the Invention
The present invention relates to a method of casting molten steel when molten steel is vibrated by the action of an electromagnetic coil. Also the present invention relates to a continuous casting apparatus for the method of casting molten steel and a cast slab which has been cast by the method and the apparatus. More particularly, the present invention relates to a method of casting molten steel, an apparatus for the method of casting molten steel and a cast slab which has been cast by the method and the apparatus, characterized in that: gas and powder trapping caused in molten metal in the process of solidification of the molten metal in a mold can be prevented; cracks on a surface of the cast slab caused when the temperature is not uniform can be prevented; and further the inner structure of the cast slab can be made fine.
2. Description of the Prior Art
As a method for making a solidification structure to be equi-axed crystal so that segregation caused in the process of solidification can be reduced, in continuous casting of steel, electromagnetic stirring is widely used. For example, this technique is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 50-23338. It is possible to obtain an equi-axed structure when molten steel in the proximity of a solidification interface is forcibly given a fluidity by electromagnetic stirring so that prismatic dendrites can be cut apart. In order to enhance an equi-axed crystal ratio, various investigations have been made into the condition of electromagnetic stirring until now and segregation has been somewhat reduced.
However, according to the conventional electromagnetic stirring generated in a mold, an equi-axed crystal ratio by which a sufficiently high quality of product can be produced is not necessarily obtained in the case of producing a type of steel (for example, a type of steel, the carbon content of which is not more than 0.1%) in which it is difficult to form an equi-axed crystal structure. In order to enhance the equi-axed crystal ratio of the above type of steel, in which it is difficult to form an equi-axed crystal structure, it can be considered to increase the thrust of electromagnetic stirring generated in a mold. However, when this method is adopted, a surface velocity of molten steel in the mold is increased, and powder trapping is caused on the surface of molten steel. As a result, a defect is caused on the surface of the product. In some types of steel in which the occurrence of segregation is severely restricted, it is impossible to meet the demand of quality only when the equi-axed crystal ratio is enhanced. In these types of steel, the grain size of the equi-axed crystal structure must be made further fine.
Conventionally, the following technique is reported, for example, the following technique is disclosed in the U.S. Pat No. 5,722,480. Pulse waves, which are generated by turning on and off an electric current, are given in an alternating static magnetic field so that an electromagnetic force directed to the center of a mold side wall is generated. By this electromagnetic force, a lubricating effect and a soft contacting effect can be provided. However, according to the above method, the electric current is not always made to flow, and an acceleration of the vibrating waves is not controlled. Japanese Unexamined Patent Publication (Kokai) No. 9-182941 discloses a method in which a stirring direction of the electromagnetic stirring is periodically inverted so that a downward flow cannot be developed and diffusion of inclusion to a lower portion can be prevented. However, according to this method, vibrating waves are not given onto the front solidified shell by a shifting magnetic field. Also, it is not a method in which acceleration is controlled so that the solidification structure can be made fine, inclusion can be eliminated for purification and the meniscus can be stabilized.
Further, according to a method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 64-71557, an electromagnetic coil for generating a magnetic field to rotate molten metal on a horizontal surface is alternated so that it can exist in a static condition. Therefore, a flow velocity of the meniscus is zero in this method. According to a method disclosed in Japanese Examined Patent Publication (Kokoku) No. 3-44858, in order to prevent V-segregation and porosity of a cast slab, in an electromagnetic stirring in which a circulation current is caused on a plane perpendicular to a direction in which a cast slab is drawn out, a stirring direction is inverted at intervals of 10 to 30 seconds. According to a method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 54-125132, the casting temperature is prescribed for preventing ridging of stainless steel and, in order to prevent positive and negative segregation caused in electromagnetic stirring, a ratio of two electric currents, the phases of which are different from each other, is prescribed, and a direction of electric current is switched and an electric current is made to flow in a predetermined direction for 5 to 50 seconds.
Further, according to Japanese Unexamined Patent Publication (Kokai) No. 60-102263, in order to prevent the occurrence of defects caused in casting steel of 9%-Ni which is used for a thick plate at low temperatures, alternating time of electromagnetic stirring is set at 10 to 30 seconds.
In the above techniques, alternating stirring is conducted in a relatively long period. That is, the above techniques are entirely different from a technique in which vibrating waves are given onto the front solidified shell by a shifting magnetic field and acceleration of the vibrating waves is controlled.
Therefore, it is desired to develop a new technique by which the above problems are solved, the solidification structure is made fine, inclusion is purified and further the meniscus is stabilized.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above problems caused in the conventional electromagnetic stirring generated in a mold. That is, it is an object of the present invention to provide a continuous casting method in which vibration is given by a shifting magnetic field so that the equi-axed crystal ratio can be enhanced without the occurrence of surface defects caused by powder trapping and the equi-axed crystal structure itself can be further made fine. Further, it is an object of the present invention to provide a continuous casting apparatus to which the above continuous casting method is applied, and also it is an object of the present invention to provide a cast slab produced by the above method and an apparatus.
It is another object of the present invention to solve problems caused in the casting method in which an electromagnetic force is given to molten metal so that solidification of molten metal can be stabilized and the surface property of a cast slab can be improved.
The summary for the present invention to accomplish the above objects is described as follows.
(1) A method for casting molten metal comprising the steps of: pouring molten metal into a mold and solidifying it in the mold while applying an electromagnetic force, which is generated by an electromagnetic coil arranged in proximity to a molten metal pool in the mold, upon the molten metal; and vibrating the molten metal, which has been solidified in the mold or is being drawn out downward from the mold while being cooled and solidified, by a shifting magnetic field generated by the electromagnetic coil so that the molten metal is alternately given a high intensity and a low intensity of acceleration.
(2) A method for casting molten metal comprising the steps of: pouring molten metal into a mold and solidifying it in the mold while applying an electromagnetic force, which is generated by an electromagnetic coil arranged in the proximit
Fujisaki Keisuke
Harada Hiroshi
Hasegawa Hajime
Sasai Katsuhiro
Takeuchi Eiichi
Kerns Kevin P.
Nippon Steel Corporation
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