Specialized metallurgical processes – compositions for use therei – Processes – Process control responsive to sensed condition
Patent
1995-12-01
1997-12-02
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Process control responsive to sensed condition
75511, 75512, C21C 710
Patent
active
056931204
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a vacuum degassing and decarburization treatment for a molten steel using a vacuum degassing equipment, and more particularly to a production method, for a low carbon molten steel, which is advantageous from the aspects of cost of production and high efficiency, using a vacuum degassing and decarburization treatment which improves the recirculating or stirring gas for a molten steel.
BACKGROUND ART
A method which exposes a molten steel to a reduced pressure by using vacuum treatment equipment (for example, RH, DH, etc.) is known as a method of degassing and decarburizing a molten steel according to the prior art. This method is a decarburization treatment method which promotes the reaction C+1/2 O.sub.2 .fwdarw.CO by reducing the pressure. The vacuum treatment equipment includes a lance and/or a twyer for blowing an Ar gas into the molten steel so as to recirculate or stir the molten steel and to promote the treatment, a double twyer for simultaneously blowing oxygen necessary for deoxidization and Ar for cooling it, and a lance and/or a twyer for blowing Ar into the molten steel so as to stir the molten steel by the resulting fine bubbles, and to promote the treatment by increasing the area of the reaction interface.
FIG. 8 shows these members of an RH vacuum treatment equipment, by way of example. In the drawing, reference numeral 27 denotes an Ar gas blast twyer for recirculating the molten steel between a molten steel ladle 21 and a vacuum degassing vessel 29, reference numeral 28 denotes an Ar gas blast twyer for stirring the molten steel, reference numeral 24 denotes an Ar gas blast twyer for recirculating the molten steel between the molten steel ladle 21 and the vacuum degassing vessel 29, and reference numeral 30 denotes a double twyer for simultaneously blowing oxygen necessary for decarburization from an inner pipe and an Ar gas for cooling the inner pipe and a refractory around the inner pipe from an outer pipe. Because the Ar gas is blown from these lances and/or twyers, vacuum degassing and decarburization treatment can be promoted.
However, there remains the problem that because Ar is extremely expensive, the production cost of the molten metal is high.
In contrast, as a method of reducing the cost by simultaneously blowing oxygen necessary for decarburizing the molten steel inside the vacuum treatment equipment and the Ar gas necessary for cooling it into the molten steel by using a double pipe, Japanese Unexamined Patent Publication (Kokai) No. 56-44711 discloses a method which blows a CO.sub.2 gas during treatment by using a single pipe in place of the double pipe. This is the method which vacuum decarburizes the molten steel by the endothermic reaction C+CO.sub.2 .fwdarw.2CO. According to the observation made by the inventors of the present invention, however, it has been found out that the decarburization reaction does not proceed below a certain carbon concentration of the molten steel even when the CO.sub.2 gas is blown into the molten steel, and a low carbon steel having a carbon concentration of below 50 (ppm) cannot be produced. It has further been found out that when a deoxidizing alloy such as Al or Si is added to the molten steel inside the vacuum treatment equipment, the oxygen concentration increases, on the contrary, when CO.sub.2 is continuously blown into the molten steel even after the addition of this alloy, so that an excessive amount of the alloy must be added to remove this oxygen, and the resulting fine oxides deteriorate the cleanness of the molten steel.
DISCLOSURE OF INVENTION
The present invention has been completed in view of the problems described above, and the gist of the present invention resides in the following points.
1. In a vaccum degassing and decarburization treatment method for a molten steel using a vacuum treatment equipment provided with a lance and/or a twyer capable of blowing a gas into the molten steel and by blowing the gas from the lance and/or the twyer, a production method for a low carbon mo
REFERENCES:
patent: 4071356 (1978-01-01), Yamamoto et al.
Patent Abstracts Of Japan, vol. 12, No. 353 (C-530), Sep. 21, 1988 & JP-A-63 111116 (Sumitomo Metla Ind. Ltd.), May 16, 1988.
Patent Abstracts Of Japan, vol. 15, No. 211 (C-836), May 29, 1991 & JP-A-03 061317 (NKK Corp.), Mar. 18, 1991.
Patent Abstracts Of Japan, vol. 10, No. 166 (C-353), Jun. 13, 1986 & JP-A-61 019727 (Sumitomo Kinzoku Kogyo K.K.), Jan. 28, 1986.
Endoh Koichi
Hayashi Fumio
Kaku Toshihiko
Moriguchi Makoto
Obana Yasuo
Andrews Melvyn
Nippon Steel Corporation
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