Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1997-04-17
1999-07-06
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
266210, C21C 710
Patent
active
059192828
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for vacuum refining a molten steel in an RH vacuum degassing apparatus, a DH vacuum degassing apparatus and the like. In particular, the present invention provides a process and apparatus for vacuum refining a molten steel which can efficiently carry out a vacuum refining reaction of the molten steel with a refining flux.
An ever-increasing demand for meeting of a strict quality requirement of products in recent years has resulted in a demand for removal of impurities on the order of ppm. To cope with this demand, an attempt to extend the use of pretreatment of molten iron and secondary refining has been made in steelmaking processes.
For example, in order to produce an ultra low sulfur steel using an RH vacuum degassing apparatus, Japanese Unexamined Patent Publication (Kokai) Nos. 5-171253, 5-287359, 5-345910, and 6-65625 and the like disclose a refining flux projection method wherein a refining flux (a desulfurizer), together with an inert carrier gas, is blown through a top-blown lance against the surface of a molten steel circulated in a tank of an RH vacuum degassing apparatus equipped with the top-blown lance and allowed to forcibly enter into the molten steel, thereby desulfurizing the molten steel.
On the other hand, the applicant of the present invention has proposed, in Japanese Unexamined Patent Publication (Kokai) No. 7-41826, a method wherein a refining flux is projected on or added to the surface of a molten steel while heating the molten steel by means of a burner in a vacuum treatment apparatus to prevent a lowering in the temperature of the molten steel and to promote the melting of the refining flux, thereby improving the desulfurization efficiency.
In the same publication, the applicant has disclosed a technique where a top-blown lance, which can simultaneously spout a fuel gas, an oxygen gas for combustion of the fuel gas, and a refining flux (with the aid of an inert carrier gas such as argon gas), more particularly a top-blown lance comprising: a fuel gas feed hole provided in the divergent face at the lower end of a Laval lance for spouting an oxygen gas; and a refining flux introduction pipe provided within the passageway (axial center) of an oxygen gas, the spout of the refining flux being open into the divergent space, is disposed ascendably and descendably in a suspended state within a vacuum degassing tank, burner flame heating by the fuel gas and the oxygen gas and the projection of the refining flux are performed to preheat the refining flux by the heat of combustion (flame) in the burner until the refining flux reaches the surface of the molten steel, thereby promoting the melting of the refining flux within the molten steel to improve the desulfurization efficiency.
Japanese Unexamined Patent Publication (Kokai) No. 5-195043 discloses a method wherein a body of a plasma torch having a plasma electrode is provided in an RH degassing tank on its side wall above the surface of the molten steel, a flux feed pipe is provided on the body of the plasma torch to feed a refining flux into a plasma jet, and the flux is heated and/or melted with the plasma jet in the course of spouting until the flux reaches the surface on the molten steel, followed by introduction into the molten steel.
As described above, according to the conventional techniques, in vacuum refining of a molten steel using a refining flux (a desulfurizer) in a vacuum degassing apparatus, the refining flux is introduced into the surface of the molten steel with the aid of an inert gas as a carrier gas, and, when a refining flux is heated, burner combustion heat treatment by using the oxygen gas and the fuel gas or heat treatment by means of a plasma jet is conducted.
The reason why an inert gas is used as a carrier gas in the introduction of a refining flux, for example, a desulfurizer, into a molten steel is as follows.
In general, the desulfurization reaction of a molten steel is expressed by the following formula: the molten steel and ( ) represents that t
Fukuda Kazuhisa
Gofuku Hiroki
Hoshijima Yosuke
Iguchi Masao
Kakizoe Hidekazu
Andrews Melvyn
Nippon Steel Corporation
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