Reference measurements in gas carburizing atmospheres: part 1

The most important parameters for the control of carburizing processes are the temperature and the C-potential of the atmosphere. Temperature is normally measured by means of thermocouples. For the control of C-potential the measurement of oxygen partial pressure of the furnace atmosphere by in-situ O2-probes and Lambda probes (L-probes) became accepted. The thermocouples as well as the probes for measurement of residual oxygen gradually lose in accuracy. Therefore, reference measurements for adjustment of temperature and C-potential are essential for an exact control. Within this article the reasons for incorrect measurements with thermocouples and O2-probes, respectively L-probes will be explained. The appropriate reference measurements for correction of these faults are also described. Furthermore, it is explained what has to be observed with these reference measurements and which information is given, thereby, about the furnace atmosphere, especially with the gas analysis by means of a gas analyzer. The first part for the article refers only to gas analysis as a reference measurement for C-potential. Within part 2, following later, reference measurements with a second O2-probe or L-probe, dew point measurement and foil test will be described.