Unterdruckaufkohlung : Modellierung und Simulation der Eindringtiefe verschiedener Aufkohlungsgase in Sacklochbohrungen. Diskussion

The paper introduces a model permitting to predict the penetration depth of propane and acetylene in blind holes in the low pressure carburizing process. The model is based on mass balances of the gas volume in the bore hole. Test calculations proved a good conformity of the calculated course of the carburizing gas concentration in the borehole with the penetration depth determined by hardness measurement. The carbon transfer rate at small propane or acetylene concentrations like they exist in the bore hole were measured and are presented. It is clearly visible that the carbon transfer rate of propane is barely distinguishable from that of acetylene, and that a satisfactory carburizing process can already be obtained with a propane or acetylene concentration of only about 20% in the gas. For application in industry, this means that even large and compact charges can be carburized by using propane, if only the propane flow rate fed to the furnace is sufficient. Model calculations show that acetylene is more suitable for carburizing blind holes than propane particularly because of the very low diffusion resistance of its decomposition product hydrogen, produced during the carburizing reaction. However, as using acetylene is more complicated and expensive than using propane, acetylene should only be used if this is absolutely necessary. The introduced model can be helpful to estimate, even before the first experiments are conducted, the maximum depth or the minimum diameter that can be carburized by propane or acetylene.