Regulating the carbon potential in a gas carburizing atmosphere with natural gas as the enriched gas, by using O sub 2 and CO sub 2 sensors

The gas-carburizing atmosphere for surface treatment of steel can be regulated using the carbon potential (CP) which is obtained by measuring dew point, O sub 2 concentration or CO sub 2 concentration. Since zirconium oxide O sub 2 sensors are easier-to-handle and respond better than others, they are generally used when measuring O sub 2 concentrations. Methane is the main component of natural gas and is stable at high temperatures, so that traces of it tend to remain in furnaces. The remaining methane decomposes on the O sub 2 sensor tip, and the O sub 2 concentration around the sensor tip decreases. Therefore the measurement of carbon potential with O sub 2 sensors has been considered to be difficult, when natural gas is used as the enriched gas. In this study, carbon potential control using O sub 2 sensors for gas-carburizing atmospheres enriched with natural gas, was examined. A new method for regulating CP was also examined. It utilizes the difference between CP calculated from the C0 sub 2 concentration and that calculated from the O sub 2 sensor value, while preventing sooting.