Sensor system for controlled carbonitriding

Carbonitriding is mainly used to enhance the hardenability and wear resistance of unalloyed steels. Last year investigations have shown that improved component properties can efficiently be obtained by carbonitriding also low alloy and even higher alloy steels. The importance of carbonitriding rises. In the past, carbonitriding was done with constant ammonia additions, e.g. 2–5 vol% are added to the carburizing atmosphere without controlling or measuring the nitriding potential of the atmosphere. The results scatter in a wide rage depending on furnace, batch size and load and many other influencing factors. The need for a control system is obvious. The presented sensor system allows carbonitriding processes, where carbon and nitrogen potentials of the atmosphere are controlled. This allows adjusting surface carbon and nitrogen contents to desired values independently and guarantees constant product quality. The sensor system consists of a combination of an ammonia and an oxygen sensor and simulation software. By this way online diffusion profile calculation for carbon and nitrogen are possible even for alloyed steels taking alloy factors for both into account. These alloy factors, measured for many steel grades and phase boundaries, were calculated with Thermocalc