Comparison of ferritic nitrocarburising technologies

Three steels of commercial grade AISI 1020, AISI 4140 and AISI 4340 have been subjected to ferritic nitrocarburising using a variety of heat treatments, such as a salt bath, fluidised bed reactor, and plasma and gaseous nitrocarburising. The effect of post-treatments on the white layer composition has been also studied. It has been found that for a given processing time, both salt bath and fluidised bed processing formed the thickest white layer. The formation of an ε monophase white layer was achieved only in the salt bath and gaseous process. It has been established that the oxidation treatment used to improve corrosion resistance of the white layer has the effect of transforming ε carbonitride to γ′.