Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1990-06-11
1992-10-13
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75560, 266162, C21C 702
Patent
active
051547562
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for the preliminary treatment such as desiliconization and dephosphorization of molten pig iron (referred herein as molten hot metal) prior to the decarburization refining of the molten hot metal for steel making.
BACKGROUND OF THE INVENTION
Known methods for the desiliconization and dephosphorization of molten hot metal for steel making which is flowing in a delivery trough of a blast furnace by adding thereto a powdered refining agent, may be roughly classified into the following 4 methods. The same classification may be made of known methods for the preliminary treatment of molten hot metal continuously caused to pass in a horizontally disposed elongated vessel from one end to another.
(1). As diagrammatically shown in FIG. 1, a top placing method wherein a powdered refining agent 2 is sprayed by its own weight on the surface of molten hot metal 1 continuously flowing in a trough.
(2). As shown in FIG. 2, a top blowing projection method wherein a powdered refining agent 2 is projected onto the surface of molten hot metal 1 continuously flowing in a trough by use of a non-oxidizing carrier gas 4 through a lance 3 disposed with its front end positioned above the surface of the molten hot metal.
(3). As shown in FIG. 3, a top blowing injection method wherein a powdered refining agent 2 is injected into molten hot metal 1 continuously flowing in a trough by use of a non-oxidizing carrier gas 4 through a lance 5 disposed with its front end positioned below the surface of the molten hot metal.
The top blowing projection method (2) above is disclosed in JP B 61-45,681.
Besides the above-mentioned methods, we have proposed in JP A 60-177,114, JP A 60-177,117 and JP A 60-181,212 wherein a powdered refining agent is injected into molten hot metal by use of an oxygen-rich gas, instead of a non-oxidizing gas, as a carrier, wherein the mixture of the oxygen-rich gas and the powdered refining agent is bottom blown through single-pipe nozzles instead of tuyeres of a double tube structure. In these methods solid products formed by reaction of the hot metal and refining agent accumulate on front ends of the single-pipe nozzles, and the injection can be efficiently carried out.
PROBLEMS IN THE ART THE INVENTION AIMS TO SOLVE
In the above-mentioned top placing method (1) the refining agent does not efficiently contact the molten hot metal, and thus, there is a problem in that it is difficult to achieve a sufficient reaction between the refining agent and the molten hot metal during the step in which the molten hot metal flows in the trough.
In the above-mentioned top blowing projection method a considerable projecting pressure is necessary in order to push the refining agent into the molten hot metal, Since a projecting pressure is naturally limited, it is advantageous to make the depth of flowing molten hot metal small and to project the refining agent so that it may reach near the bottom of the flow. In that case, however, the refractory of the trough bottom inevitably suffers from melt-loss immediately below the portion where the projection is made. If a projection is too shallow to invite melt-loss of refractory, a satisfactory effect of the projection is not obtained.
The above-mentioned top blowing injection method (3) poses the same problem as the method (2) of melt-loss of refractory immediately below the portion of the injection and an additional problem of melt-loss of the lance 3 in itself.
Furthermore, by the methods (1) to (3) above, no satisfactory results of refining are achieved with commercially acceptable refining time and amount of the powdered refining agent used. For example, while these methods may desiliconize molten hot metal to a level of [Si]=0.10 to 0.15% by weight, they cannot practically realize [Si]=trace. This is related to the fact that these methods cannot achieve agitation and admixing of the molten metal and refining agent enough to ensure a sufficient reaction thereof.
On the other hand, according to t
REFERENCES:
patent: 3406027 (1968-10-01), Bonilla
patent: 4515630 (1985-05-01), Tyler
Fukami Yasutami
Nakajima Yoshio
Nisshin Steel Co. Ltd.
Rosenberg Peter D.
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