Metal treatment – Compositions – Heat treating
Patent
1990-06-26
1991-10-15
Yee, Deborah
Metal treatment
Compositions
Heat treating
148 203, C21D 900
Patent
active
050571648
ABSTRACT:
Process for thermal treatment of metals by passage of metallic pieces into an elongated zone under a controlled atmosphere, having an upstream section at an elevated temperature, where the controlled atmosphere comprises nitrogen and reductive chemicals, particularly hydrogen, possibly carbon monoxide; and a downstream section at a lower temperature under a controlled atmosphere. The invention is characterized by the fact that in the upstream section at an elevated temperature, the atmosphere comprises nitrogen having a residual content of oxygen between 0.5% and 5% produced by separation of air using permeation or adsorption techniques. The reductive chemicals are present at all times in a content at least sufficient to eliminate the oxygen admitted with the nitrogen. The controlled atmosphere in the section downstream from the elongated thermal treatment zone is formed by admission of a gaseous flow taken from the upstream section at an elevated temperature and transferred directly into the downstream section at a lower temperature.
REFERENCES:
patent: 4445945 (1984-05-01), Schwalm
Duchateau Eric
Nilsson Tom
Rancon Yannick
L'Air Liquide Societe Anonyme pour l'Etude et, l'Exploitation de
Yee Deborah
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