Plasma ferritic nitrocarburising of carbon and low alloy 0·4%c steels in N 2 –H 2 atmospheres with CO 2 gas additions

Abstract

Plasma ferritic nitrocarburising of carbon and low alloy 0·4%C steels was carried out at 570°C in a N₂–H₂ atmosphere containing CO₂ gas additions. The influence of the atmosphere composition, the duration of treatment, and the composition and microstructure of the steels on the phase composition of the compound layer was investigated. The formation of a monophase ɛ compound layer was not possible with the parameters used in this study. The phase composition of the compound layer was found to be very dependent on the amount of CO₂ in the process gas. A difference in the plasma nitrocarburising behaviour of the two low alloy steel grades was observed, and the formation of some austenite in the diffusion zone of one of the steels, at the interface with the compound layer, is proposed to explain this observation.