Carbonitriding is used to improve the properties of steel components. The carbon and nitrogen content and the microstructure comprising martensite, retained austenite, and finely distributed nitrides and carbides are significant parameters determining component properties. Current state of the art posits that these multi-phase microstructures determine optimal material conditions. The reliability of a process is strongly dependent on the options for control. Previous studies dealt with the measurement of atmospheric nitrogen potential by means of an ammonia sensor in the exhaust gas. The equilibrium contents in the austenite were determined based on this and the mutual effects of carbon and nitrogen. Further improvement of the reliability of the carbonitriding process requires simulation of the carbon and nitrogen profiles and the precipitation condition of carbides and nitrides. Apart from the equilibrium content, the maximum solubilities determined by phase diagram calculations and precipitation in the presence of interdependent carbon and nitrogen effects, including interactions with other alloying elements, need to be examined towards further development of controlled carbonitriding to ensure reliable heat treatment results.