Monitoring and Control of Hydrogen-Bearing Protective Gas Atmospheres - Sensors and Their Function

In heat treating, the treatment of metals in a hydrogen-bearing protective gas atmosphere is to avoid oxidation. Likewise, depending on the process, this atmosphere needs to provide a mass transfer of carbon (carburizing) or nitrogen (nitriding) or both (carbonitriding/nitrocarburizing) into the surface of the parts. However, there are processes where mass transfer should be avoided. For example, in neutral hardening and annealing of low alloy steels the resulting mass transfer will cause carburization or decarburization of the part surface. For bright annealing of high alloyed steels, a gas with an extremely low dew point or oxygen partial pressure must be used. Concerning these processes, the focus is to create and maintain an atmosphere with a reducing effect. To achieve this, installing a tight measurement and control system is mandatory for the final quality of the work parts.

In this presentation, we begin with an overview on how atmospheres are created and what they are composed of, what atmosphere potentials have to be followed, and their interaction with the material to be treated.

Finally, we describe how to measure and control such potentials in an automated way.