Nitrogen transfer in low-pressure carbonitriding processes

For some years now, low-pressure carburising with acetylene has been an integral part of case hardening operations in the gear and aircraft industry as well as in some commercial heat treatment shops. Case hardening under vacuum will be even more interesting for the relevant industries once low-pressure carbonitriding has successfully completed its development phase and is available for industrial utilization. While the important factors in low-pressure carburising with acetylene have been thoroughly examined for their influence on carbon transfer [1, 2, 3, 4], the mechanism of nitrogen transfer in low-pressure carbonitriding is still largely unknown. Therefore, a research programme was initiated to examine the influence of process parameters such as gas pressure, temperature and process duration as well as the type of case-hardening steel on the transfer of nitrogen. For the nitrogen supply source ammonia gas was used. The paper presents process fundamentals and measures how to influence the achieved nitrogen profiles.