Latest research projects have shown that retained austenite, if stabilized by nitrogen, has a positive impact on the fatigue strength of work pieces. The amount of retained austenite is a function of the process temperature and, more importantly, the combined diffusion profile of carbon and nitrogen applied during the carbonitriding process. But up till now, only the carbon potential is controlled and even that is not easy to achieve.

This paper will present a new system capable of measuring and controlling both the carbon potential and nitrogen potential independently. Based on the activities of nitrogen and carbon in iron and the effect of alloying elements on such activities as well as the solubilities, this system offers a practical approach for applying potentials on real steels.