NEW DEVELOPMENTS IN GASEOUS FERRITIC NITROCARBURISING BY USING HYDROCARBON GASES
AbstractIndustrial gaseous ferritic nitrocarburising processes, or shortly named „fnc“, use mainly carbon dioxide or endothermic gas as the carbon providing gas in addition to ammonia gas. Both processes have positive and negative aspects and produce somewhat different layer structures. The carbon dioxide fnc process depicts a faster layer growth yielding a thicker and more porous nitride layer, whereas the endothermic fnc process produces a nitride layer with higher carbon content and a larger proportion of the å-nitride phase. A newer variant of a fnc process uses hydrocarbons, and preferably propane or natural gas, as carbon providing gas replacing partly or totally carbon dioxide gas. This newer process uses different single or double step cycles combining the advantages of the enhanced nitrogen transfer as created by the carbon dioxide variant with the increased carbon transfer rate of the endothermic gas. This results in faster layer growth producing nitride layers with higher carbon content and a larger proportion of the å-phase. This is advantageous with respect to wear resistance of the nitrocarburised components. In addition, it improves furnace productivity.