Effect of cooling rate on plasma nitrocarburised compound layers for pure iron

Plasma nitrocarburising was carried out with various CO gas compositions with 3 mbar at 570degreesC for 3 hours. After treatment, different cooling rates (fast cooling, slow cooling and gas cooling) were used to investigate their effect on the structure of the compound layer, the epsilon phase being the outer part of the compound layer and the gamma' phase being the inner pail. The CO gas composition influenced the constitution of the compound layer produced, i.e. high CO contents were essential for the production of an c phased compound layer, as did a variation of the cooling rate, with a large amount of gamma' phase transformed from the epsilon phase during slow cooling. The transformation was reduced with an increasing cooling rate and prevented by a fast cooling rate of approximately 18.5degreesC/sec at 500degreesC, at which temperature this transformation began.