Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1993-03-11
1994-07-26
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75511, 75512, C21C 710
Patent
active
053324170
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for decarburisation of steel in a vacuum treatment chamber and a vacuum treatment chamber for implementing the method.
In order to treat steel from the converter in which it is produced, it is known to use a vacuum treatment chamber, widely known as RHOB (Rheinstahl Heraus Oxygen Blowing).
A chamber of this type is used to perform decarburisation treatments or a dehydrogenation as well as mild treatments consisting in producing a steel in which the ranges of the various additives are reduced to such a point that it is impossible to obtain it directly in the converter.
It is known to use a vacuum treatment chamber consisting of three parts: which are immersed in the steel ladle containing the steel to be treated.
During the decarburisation treatment of the steel, that is to say the treatment which gives it a carbon content of less than 40 ppm, it is known to inject a certain amount of oxygen over the bath of metal contained in the treatment chamber.
Thus, the carbon contained in the bath of metal to be treated reacts with the oxygen supplied according to the reaction:
The oxygen is conveyed to the level of the bath of molten metal to be treated by means of a lance which is immersed in the treatment chamber.
The drawback of this method lies in the fact that oxygen is blown vertically relative to the walls of the treatment chamber, that is to say it never enters into direct contact with the vertical walls of the chamber on which deposits of metal are formed due to the splashes originating from the bath of metal during treatment.
These deposits, known as build-up, accumulate in the treatment chamber, end up by increasingly restricting the free part of the chamber and can prevent the passage of the treatment lance.
Moreover, the deposits on the walls of the chamber contain a certain amount of carbon depending on the carbon content of the steel during previous treatments.
Thus, during decarburisation treatments, the metal to be treated sweeps over these deposits during its circulation in the intermediate ring of the chamber, this circulation being due to the blowing of a neutral gas in one of the legs with which the bottom part of the said chamber is equipped.
A proportion of the deposit is thus remelted, which may give rise to recarburisation of the metal to be treated in the chamber.
It is thus necessary to remove these deposits by means of a treatment, called slag-out, in which oxygen is blown directly onto the build-up in order to form an iron oxide which falls into the base of the shaft.
Such a slag-out treatment is necessary approximately every 15 treatments of steel in the chamber.
A further drawback lies in the leaktightness required at the level of the passage of the treatment lance into the upper part of the chamber. In fact, as the chamber has to be kept under vacuum during the treatment, leaktightness is very difficult to achieve.
The aim of the present invention is to provide a method for decarburisation of steel in a vacuum treatment chamber consisting of an upper part in the shape of a bell, of an intermediate ring in which the bath of metal to be treated is located and of a lower part equipped with two legs which are immersed in a steel ladle containing the steel to be treated, into which oxygen is blown horizontally over the bath of metal to be treated.
The present invention also relates to a vacuum steel-treatment chamber for implementing the above method, in which at least two horizontal tuyeres are provided in the intermediate ring of the said chamber, substantially in the centre of the latter.
BRIEF DESCRIPTION OF THE DRAWING
The figure shows a sectional view of a vacuum treatment chamber according to the invention.
DETAILED DESCRIPTION
The features and advantages will become apparent during the description which follows, given solely by way of example and given with reference to the appended drawing showing a sectional view of a vacuum treatment chamber according to the invention.
The method for decarburisation of steel according to the invent
REFERENCES:
patent: 4071356 (1978-01-01), Yamamoto
patent: 4104057 (1978-08-01), Maas et al.
Gmelin Handbook, vol. A, No. 9, p. 191A; Gmelin-Durrer: "R.H.O. Process".
Patent Abstracts of Japan, vol. 14, No. 57 (C-684)(4000), Feb. 2, 1990, abstract No. 1-283316.
Rosenberg Peter D.
Sollac
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