Ferritic nitrocarburizing accomplishes surface treatment of a part in the ferrite region of the
iron-carbon equilibrium diagram. As the process takes place in the ferrite region, both
nitrogen and carbon diffuse into the steel surface. The process is categorized as a
Andrea B. Szilágyi
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thermochemical treatment and is carried out at temperatures between 525°C and 650 °C,
the typical process temperature is approximately 565 °C.
Ferritic nitrocarburizing improves the surface characteristics of plain carbon steels, lowalloy
steels, cast irons, and sintered ferrous alloys: resistance to wear, fatigue, and corrosion
are improved with the introduction of nitrogen and carbon.
Treatment time of gaseous ferritic nitrocarburizing is generally between 1 to 4 h.
Although there are a number of proprietary gas mixtures, most contain ammonia (NH3) and
an endothermic gas. As in gas nitriding, the cracked nascent ammonia gas will dissociate at
the steel surface and react with the hydrocarbon gas to form both nascent nitrogen and free
carbon. The gases will allow carbon dioxide to be generated in relation to the classical
water gas reaction (Eq. (3)).
CO H CO H O 22 2 (3)
The carbonmonoxide is not stable, and form carbondioxide as shown in Eq. (4)
CO CO CO C 2 (4)
The nascent carbon will diffuse to the surface. The primary objective of the ferritic
nitrocarburizing process is to form nitrides and, most importantly, surface carbon, which
will encourage the ε-nitride phase in the surface of the steel. The metallurgical results of the
process are very similar to the classical nitriding process, with the exception that now there
is carbon in the layer.