L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des

Tom Nilsson

Eric L Duchateau

Yannick Rancon

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.

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Helsingborg, Sweden

Tom Nilsson