Casting flux

Details Casting flux Casting flux

1994-11-18

1998-07-21

Andrews, Melvyn

Specialized metallurgical processes, compositions for use therei

Compositions

Solid treating composition for liquid metal or charge

75323, 75329, C22B 910

Patent

active

057829560

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a casting flux for steels or alloys on an iron, nickel or cobalt basis which makes heavy demands on the degree of oxidic purity for continuous or ingot casting. The term casting flux in this case also includes powders for the capping and after-treatments of metal melts in ladles or intermediate vessels.
The casting fluxes hitherto used in practice are built up on a silicate basis, containing as main component 20 to 40% by weight SiO.sub.2, in addition to CaO and Al.sub.2 O.sub.3. In connection with Na.sub.2 CO.sub.3 and CaF.sub.2 and in some circumstances B.sub.2 O.sub.3, in addition to other important properties the low melting temperature required for casting is set below 1200.degree. C., the necessary viscosity being in the range of approximately 1 Pa.s, with a vitreous state at temperatures below 800.degree. C. In addition these casting fluxes also contain other oxides, such as iron and manganese oxide and also P.sub.2 O.sub.5, which are introduced via the raw materials. In some cases they are also deliberately added to obtain the aforementioned properties to the required extent. Casting fluxes are also used in industry which in order to maintain a vitreous solidification up to as low temperatures as possible contain increased SiO.sub.2 contents with a low CaO/SiO.sub.2 ratio below 1.0, to prevent crystalline precipitations, for example, cuspidin or nephelin, from the vitreously solidifying casting slag in the casting gap.
Due to their relatively low thermodynamic formation energy, these casting fluxes on a silicate basis with additions of Na.sub.2 CO.sub.3 and in some cases B.sub.2 O.sub.3 and also iron and manganese oxides have a considerable oxidation potential in relation to steels and alloys on an iron, cobalt and metal basis with a low oxygen content. Reaction with alloying elements, such as aluminium, titanium and others causes non-metallic inclusions in the solidified metal due to which the degree of oxidic purity and therefore the properties of use of these metals may considerably deteriorate. Hitherto there has been no technically feasible way of achieving the necessary low oxidation potential of the components of the casting flux without abandonment of the components hitherto used, which more particularly effect vitreous solidification down to low temperatures.
U.S. Pat. No. 3,926,246 discloses the addition of controlled proportions of alkali metal oxides and phosphorus pentoxide in addition to the components normally found in casting fluxes, such as fluorides, alkaline earth oxides, aluminium oxide, silicon oxide, lithium oxide and boron oxide. The result is a substantial and in the case of certain compositions a complete vitrification of the casting flux slag, while maintaining flowability, softening behaviour and aluminium oxide absorptivity. However, although the very high additions of alkali oxides, phosphorus pentoxide, silicon oxide and boron oxide, for example, 18-24% Na.sub.2 O or 40% P.sub.2 O.sub.5 and 25% SiO.sub.2 alongside 20% P.sub.2 O.sub.5 ensure the required vitrification of the casting slag, while maintaining the other aforementioned properties, they lead to a heavy yield of oxygen from the casting slag to the liquid steel, thereby causing a considerable deterioration in the degree of purity of the continuously or ingot cast steel by the formation of non-metallic inclusions.
Similarly to the known casting fluxes, known distributor capping bodies and ladle stopper slags consist of silica or basic oxides and, just like the casting fluxes, have a considerable oxidation potential in relation to steels and alloys on an iron, cobalt and nickel basis with a low oxygen content. Thus, when these ancillary materials are used, the reaction with the alloying elements, such as aluminium, titanium, non-metallic inclusions contained in the steel produces in the liquid metal inclusions which enter the chill mould during the subsequent casting process and lead to a contamination of the metal.
In contrast, it is an object of the invention to develop a metallurgical

REFERENCES:
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patent: 3926246 (1975-12-01), Corbett et al.
patent: 3964916 (1976-06-01), Armistead
patent: 4092159 (1978-05-01), Uher
patent: 4235632 (1980-11-01), Uher et al.
patent: 4508571 (1985-04-01), Nakato
patent: 5028257 (1991-07-01), Tomkins
patent: 5356454 (1994-10-01), Itoyama
patent: 5366535 (1994-11-01), Heaslip et al.
P. Hammerschmid et al, "Untersuchungen vur . . . Giesspulver", vol. 111, No. 9, Sep. 13, 1991, Dusseldorf, pp. 97-100.

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