Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1997-03-28
1999-05-11
Ryan, Patrick
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75507, 75392, 75414, 75433, 75 59, 75 60, 75 49, C21C7/00
Patent
active
059023740
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INTENTION
1. Field of the Invention
The present invention relates to a vacuum refining method for molten steel. More particularly, the present invention relates to a vacuum refining method for refining molten steel with a straight barrel type vacuum vessel having no vessel bottom.
2. Description of the Related Art
In a vacuum refining furnace, oxygen gas is blown onto molten steel to be refined by means of top-blowing. The objects of blowing oxygen gas by means of top-blowing are described as follows. The first object is "decarburization" in which oxygen gas is reacted with carbon contained in the molten steel when oxygen gas is blown. The second object is "Al heating" in which the temperature of molten steel is raised when Al added to molten steel is burned by oxygen gas blown onto the molten steel by means of top-blowing. The third object is "desulfurization" in which flux, such as lime, is added to molten steel together with carrier gas. The fourth object is "burner heating" in which oxygen gas and combustion improving gas of a hydrocarbon, such as LNG, are blown by means of top-blowing so as to heat a vacuum vessel and suppress the adhering metal.
Conventionally, DH is known as a vacuum refining furnace composed of a straight barrel type vacuum vessel and a dipping snorkel. However, in the case of DH, a vacuum vessel to circulate molten steel goes up and down, and no molten steel exists in the vacuum vessel when it is moved to the uppermost position. Accordingly, in the case of blowing oxygen gas by means of top-blow, oxygen gas directly collides with the bottom of the vacuum vessel. Therefore, refractory material of the vessel bottom is severely damaged by the colliding oxygen gas. For the above reason, a method of blowing oxygen gas from a top-blowing lance has not been adopted at all.
Although it is not a case of vacuum refining, a secondary refining furnace in which the top-blowing of oxygen gas is conducted with a straight barrel type dipping snorkel is described as "CAS-OB Method" in S1086 of vol. 71 of "Iron and Steel" published in 1985. The object of the above method is to raise the temperature of molten steel by burning Al. However, the following problems may be encountered according to the above method. In the above method, it is impossible to conduct pressure reduction processing. Accordingly, when it is necessary to conduct a very low carbon steel melting processing and a dehydrogenation processing together with "Al heating", it is necessary to provide another refining furnace, so that the equipment cost is increased. Since the operation is conducted under atmospheric pressure, molten steel can not be sufficiently agitated, and the heat transfer efficiency is low. In order to improve the heat transfer efficiency, it is necessary to extend the processing time.
In the decarburizing reaction treatment conducted for producing ultra low carbon steel by means of top blown oxygen in a region, the carbon concentration is not more than 0.1%. Since the carbon concentration is very low, oxygen gas which has been blown out by means of top-blowing temporarily generates an iron oxide on the surface of molten steel, and this iron oxide reacts with and is reduced by carbon contained in the molten steel. In order to facilitate the reducing reaction, it is necessary to raise the hot point so as to form an advantageous condition from the viewpoints of thermodynamics and reaction speed. Therefore, it is necessary to conduct a so called hard-blowing operation in which the top-blown oxygen is made to collide with the surface of molten steel at high jet intensity.
With regard to a molten steel refining method in which an RH type vacuum refining apparatus having a vessel bottom is used and a water-cooled type top-blowing lance inserted into a vacuum vessel from an upper portion blows out a jet stream of oxygen into the vacuum vessel for refining molten steel, an example is shown in Japanese Unexamined Patent Publication No. 2-54714. Therefore, this molten steel refining method is well known.
FIG
REFERENCES:
patent: 3971655 (1976-07-01), Takashima et al.
patent: 5304231 (1994-04-01), Kato et al.
"CAS-OB Method" in S1086 of vol. 71 of "Iron and Steel", published in 1985.
"ASM Handbook", Formerly Ninth Edition, Metals Handbook, vol. 15, Casting.
Fujiwara Kunihiko
Kitamura Shinya
Miyamoto Ken-ichiro
Sasakawa Shinji
Yonezawa Kimitoshi
Elve M. Alexandra
Nippon Steel Corporation
Ryan Patrick
LandOfFree
Vacuum refining method for molten steel does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Vacuum refining method for molten steel, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vacuum refining method for molten steel will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-243450