Improvement of wear and corrosion resistance of ferrous alloys by post-nitrocarburizing treatments
Abstract
Improvement of wear and corrosion resistance
of ferrous alloys by
post-nitrocarburizing treatments
R. Sola, R. Giovanardi, P. Veronesi, G. Poli
References
Gas nitrocarburizing and post-oxidation
treatments were performed on 42CrMo4 and
20MnCr5 steels, G30 and GS600 cast irons,
to improve wear and corrosion resistance. In
both materials the thickness of the compounds
layer, mainly composed by e- and g’- phase,
resulted about 15-20 μm and the measured
diffusion layer was about 150 μm thick. A
subsequent oxidizing step, followed by
impregnation with a two different lubricating
oils was performed in order to further
enhance corrosion resistance. Wear
resistance against alumina was measured
using a ball-on-disk tribometer and the
corrosion characteristics of the samples were
studied using salt spray test in accordance
with ASTM B117. Experimental results show
that the nitrocarburizing treatment improves
significantly the wear resistance of the steels
but not the wear resistance of the studied cast
irons. The steels present almost the same
tribological behaviour, ascribable to the
formation of similar compounds, while cast
irons present different wear resistance due to
their chemical composition and the graphite
morphology. The application of
nitrocarburizing alone does not significantly
improve corrosion resistance and it may even
promote localized corrosion. The subsequent
post-oxidation step leads to a slight decrease
of the corrosion rate, because it partially seals
the porous nitrocarburized layer. The final oil
impregnation step resulted much more
effective in further decreasing the corrosion
rate and this final treatment in some cases
improves also the wear resistance.
treatments were performed on 42CrMo4 and
20MnCr5 steels, G30 and GS600 cast irons,
to improve wear and corrosion resistance. In
both materials the thickness of the compounds
layer, mainly composed by e- and g’- phase,
resulted about 15-20 μm and the measured
diffusion layer was about 150 μm thick. A
subsequent oxidizing step, followed by
impregnation with a two different lubricating
oils was performed in order to further
enhance corrosion resistance. Wear
resistance against alumina was measured
using a ball-on-disk tribometer and the
corrosion characteristics of the samples were
studied using salt spray test in accordance
with ASTM B117. Experimental results show
that the nitrocarburizing treatment improves
significantly the wear resistance of the steels
but not the wear resistance of the studied cast
irons. The steels present almost the same
tribological behaviour, ascribable to the
formation of similar compounds, while cast
irons present different wear resistance due to
their chemical composition and the graphite
morphology. The application of
nitrocarburizing alone does not significantly
improve corrosion resistance and it may even
promote localized corrosion. The subsequent
post-oxidation step leads to a slight decrease
of the corrosion rate, because it partially seals
the porous nitrocarburized layer. The final oil
impregnation step resulted much more
effective in further decreasing the corrosion
rate and this final treatment in some cases
improves also the wear resistance.
