Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1999-10-01
2001-04-03
King, Roy V. (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S579000, C148S633000, C148S668000, C148S669000
Reexamination Certificate
active
06210499
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of bright annealing metals having a high affinity to oxygen in a hood-type furnace or the like under a protective gas.
DESCRIPTION OF THE PRIOR ART
Medium- to high-alloy steels, non-ferrous metals and metals which in general are difficult to bright-anneal and have components with a high affinity to oxygen, e.g. chromium, manganese, silicon, titanium etc., have so far been subjected to a heat treatment, in order to mold their structure or recrystallize their microstructure after the molding steps. This is usually done in hood-type furnaces with non-enclosed understructure, where hydrogen or a mixture of hydrogen and nitrogen is used as protective gas. Due to the contact with the isolation of the understructure in the furnace oxygen residues are, however, transported by the hydrogen to the batch to be treated, e.g. to strip coils. The hydrogen resulting from the reaction will then oxidize the surface of the material to be annealed, where a further deficiency results from the fact that oxygen residues in the protective gas react with the surface of the material to be annealed.
When a hood-type furnace with an enclosed understructure is used, annealing may be performed under lowest dew points, but visible, disturbing oxidation residues may still remain at the metal surface of the material to be annealed.
Finally, the pure, extremely reducing hydrogen may reducingly attack the oxides of the annealing box, i.e. for instance of the heat-resistant steel construction of the understructure, the protective hood, the understructure fan, arid the distributor as well as existing scale, and transport the resulting moisture to the material to be annealed. By packing the material to be annealed in films, for instance, or by covering it with caps of steel that is free from elements having a high affinity to oxygen, a residual discoloration of the material to be annealed can not completely be repressed either.
In addition, lubricant residues from the preceding molding operations may still be present on the surface of the material to be annealed, which lubricant residues chiefly consist of water and oil, i.e. an emulsion, and evaporate during heating and react with the surface of the material to be annealed. Even by supplying a large amount of protective gas, residual discolorations can therefore not be avoided.
SUMMARY OF THE INVENTION
REFERENCES:
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patent: 5685088 (1997-11-01), Nakamura
patent: 5772428 (1998-06-01), Van Den Sype et al.
patent: 5785774 (1998-07-01), Van Den Sype et al.
Ebner Peter
Lochner Heribert
Collard & Roe PC
Coy Nicole
King Roy V.
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