Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1995-08-21
1998-06-09
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75382, 75543, 75582, 75378, 266 88, 266 89, 266157, 266207, 266227, 266229, C21C 704
Patent
active
057626820
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of processing ferrous metals including the heating of, and removal of sulphur from, a molten ferrous metal.
The molten ferrous metal is heated by the energy produced in an exothermic reaction between heating agents. The heating agents are usually oxygen gas blown onto the surface of the ferrous metal and aluminium (or silicon) dissolved in the molten ferrous metal. Aluminium (or silicon) is added to the molten ferrous metal at a controlled rate, whilst oxygen gas is simultaneously blown onto the surface of the ferrous metal at a controlled rate. However, in steel making the surface of the molten ferrous metal is covered with a layer of slag which inhibits the dissolving of the aluminium (or silicon) in the ferrous metal, and the transfer of oxygen gas to the surface of the ferrous metal, thereby reducing the efficiency of the heating process.
Sulphur is removed from the ferrous metal once it has been deoxidised. Desulphurisation is achieved by a chemical reaction between the sulphur dissolved within the molten ferrous metal and the slag thereon and, usually, injection of lime/spar and/or calcium containing agents such as calcium silicide. It is therefore desirable to have the maximum possible slag/molten metal contact surface for desulphurisation. As the sulphur content of the molten ferrous metal is reduced, its tendency to absorb nitrogen from the atmosphere increases. The absorption of nitrogen can have a detrimental effect on the properties of the finished product and it is therefore necessary to prevent or minimise the flow of nitrogen (or air containing nitrogen) across the surface of the molten ferrous metal during desulphurisation so as to minimise the pick-up of nitrogen by the metal.
The present invention provides a method of processing ferrous metals wherein the molten ferrous metal is stirred by bubbling a gas through the molten ferrous metal. A ring is then partially immersed in the molten ferrous metal within a substantially slag free portion of the surface of the molten ferrous metal to form a bounded substantially slag free area. The molten ferrous metal is heated by the introduction of exothermically reacting heating agents to the said slag free area and, the said ring is removed from the molten ferrous metal when the ferrous metal has reached a pre-determined temperature. Air is then excluded from the volume above the molten ferrous metal and sulphur removed therefrom.
Preferably the exothermically reacting agents are oxygen gas and granulated aluminium or ferro-silicon or a mixture thereof
Preferably the method of the invention is such that air is excluded from the volume above the molten ferrous metal by placing a cover thereover and maintaining the volume at a higher pressure than that of the surrounding atmosphere.
The present invention also provides apparatus for processing ferrous metals including a receptacle for receiving the molten ferrous metal, a gas supply for bubbling gas through the molten ferrous metal, a moveable ring for defining a bounded substantially slag free area on the surface of the molten ferrous metal, and a moveable receptacle cover for excluding air from the volume above the surface of the molten ferrous metal; wherein the bubbling gas produces a substantially slag free portion on the surface of the molten ferrous metal, the said ring is moveable between a first position such that it is partially immersed in the molten ferrous metal substantially within the slag free portion produced by the bubbling gas and a second position such that it is separated from the molten ferrous metal, the receptacle cover is movable between a first position such that it excludes the surrounding atmosphere from the volume above the molten ferrous metal and a second position such that the volume is open to the surrounding atmosphere, and the receptacle cover and said ring are moveable independently of each other.
Preferably the apparatus of the present invention further includes control means for controlling the rate of supply of heating agents and
REFERENCES:
patent: 3469740 (1969-09-01), Crowe
patent: 3650517 (1972-03-01), Messing
patent: 4401464 (1983-08-01), Tivelius
patent: 4518422 (1985-05-01), Metz
Steel Times-Incorporating Iron & Steel, Sep. 1993, London, GB, pp. 391-392, E. Morikawa et al. `Recent developments in the IR-UT ladle treatment process`, fig. 1.
Stahl Und Eisen, vol. 109, No. 22, 10 Nov. 1989, pp. 1089-1094; G. Stolte et al., `Das CAS/CCAS-OB-Verfahren`, see figs. 1,2,7 pp. 67-72.
Patent Asbtracts of Japan, vol. 7, No. 213 (C-187) (1358) 20, Sep. 1983 & JP,A,58 110 168 (Daido Tokushuko) 1 Jul. 1983, see abstract.
Patent Abstracts of Japan, vol. 15, NO. 393 (M-1165) 4 Oct. 1991 & JP,A,03 161 160 (Nippon Steel) 11 Jul. 1991, see abstract.
Andrews Melvyn
Vacmetal Limited
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