Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2002-02-15
2004-02-17
Zimmerman, John J. (Department: 1775)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C266S046000
Reexamination Certificate
active
06692593
ABSTRACT:
This application claims the priority of German application No. 101 08 057.3, filed Feb. 20, 2001, the disclosure of which is expressly incorporated by reference herein.
BACKGROUND AND SUMMARY OF INVENTION
The present invention relates to a method for quenching metallic workpieces in a furnace space, especially at above-atmospheric pressure. An inert gas or a mixture of inert gases, especially nitrogen, argon and/or helium are a used as quenching gas (mixture), after the metallic workpiece has been subjected to a heat treatment process in an evacuated furnace space.
Generic methods for quenching metallic workpieces are known. At high temperatures, especially at temperatures above 700° C., metals react very sensitively to oxygen. For example, at 1000° C., chromium is oxidized already at an oxygen partial pressure of about 10
−23
bar. Moreover, higher contents of, for example, titanium, result in an undesired formation of nitride, because of which heat treatment cracks can occur.
For a large number of quenching processes, a forming gas is used, which consists of about 5% hydrogen and about 95% nitrogen. By this forming gas, a slight surface oxidation is achieved on the metallic material that is to be treated and, moreover, the work is carried out below the explosive limit.
It is an object of the present invention to create a method for quenching metallic workpieces, for which annealing colors and oxidation phenomena at the surfaces of metallic workpieces can be reduced or avoided. Moreover, the absorption of nitrogen, as well as the nitride formation mentioned, are to be reduced.
REFERENCES:
patent: 4867808 (1989-09-01), Heilmann et al.
patent: 0495151 (1992-07-01), None
patent: 58-147514 (1983-09-01), None
patent: WO 89/12111 (1989-12-01), None
Linde Aktiengesellschaft
Zimmerman John J.
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