Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1996-05-20
1999-02-09
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75705, 75957, 266209, C21C 710
Patent
active
058688161
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to the smelting of liquid steel. It applies particularly to the smelting of high-purity steels having extremely low contents of carbon, or indeed also of nitrogen and of oxygen.
The use of vacuum reactors of the type called "RH" is commonplace nowadays in the smelting of liquid steel. It will be recalled that these reactors are composed: with refractories, the upper part of which vessel is connected to a gas-sucking device capable of maintaining in this vessel a reduced pressure which may go down to at least 1 torr when the reactor is operating; which are internally and externally lined with refractories, one of the ends of which emerges in the bottom of the vessel; one of these dip tubes is furnished with a device enabling a gas, usually argon, to be blown thereinto.
These plants are used as follows. The ladle containing the liquid metal to be treated is brought under the RH and the lower ends of the dip tubes are immersed thereinto. After this, a vacuum is created in the vessel, which causes a certain quantity of metal inside it to be sucked out. Finally, the blowing of gas into the dip tube equipped for this purpose commences. The function of this blowing is to drive the metal lying in this dip tube toward the vessel, and for this reason this dip tube is called "ascending dip tube". The metal travelling through the vessel next redescends into the ladle using the other dip tube, called "descending dip tube". A continuous circulation of metal between the ladle and the vessel is thus obtained. Throughout the duration of the treatment (namely, in general, from about ten to about thirty minutes), any one same drop of metal therefore resides a number of times within the vessel. The average duration of these is a function of the flow rate of the metal in the dip tubes and of the ratio between the respective volumes of the ladle and the vessel. Passing the liquid metal into the vessel maintained under vacuum principally makes it possible to decrease its contents of dissolved hydrogen and, to a lesser extent, of dissolved nitrogen. The other metallurgical operations which may occur in the vessel are: already dissolved in the metal or which is blown into it for this purpose via a lance or tuyeres inserted into the wall of the vessel; air and from the ladle slag, and therefore with optimum efficiency; then oxygen is blown thereinto and the resulting oxidation of the aluminum causes this reheating.
At the same time, the circulation of metal between the ladle and the vessel causes gentle agitation of the metal in the ladle, this being favorable to proper settling-out of the nonmetallic inclusions.
In recent years, there has been an increasing demand from steel-consuming industries for ferrometallurgical products having an extremely low carbon content (less than 50 ppm), in particular for cold-rolled sheet having high ductility and high tensile strength, for deep-drawing steels, for chrome-molybdenum ferritic stainless steels, etc. It has quickly become apparent that the RH is the in-ladle metallurgy reactor best suited to obtaining such steels under industrial conditions. In fact, the decarburization kinetics therein is favorably influenced by the massive injection of gas through the ascending dip tube, or even also into the vessel. Thus, for a ladle containing 300 t of liquid steel, an RH vessel containing 15 t of it and a flow rate of 240 t/min, a treatment time of 10 minutes may suffice to lower the carbon content in the steel from 300 ppm to 20 ppm.
The increase in demand for steels of greater and greater purity will, in the very near future, probably make it necessary to be able to obtain routinely even lower carbon contents (from 5 to 10 ppm) with a productivity at least equivalent to that of current plants (approximately 10 t/min in large integrated factories). Now, in conventional RHs, a distinct slowing down of the decarburization kinetics is observed when the average carbon content of the liquid steel becomes less than 30 ppm. Substantially speeding up sai
REFERENCES:
patent: 3321300 (1967-05-01), Worner
patent: 3367396 (1968-02-01), Sickbert et al.
patent: 3901305 (1975-08-01), Balevski et al.
Gaye Henri
Michard Jean Alex
Roth Jean-Luc
Andrews Melvyn
Cole Thomas W.
SOLLAC (Societe Anonyme)
LandOfFree
Process for adjusting the composition of a liquid metal such as does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for adjusting the composition of a liquid metal such as , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for adjusting the composition of a liquid metal such as will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1945603