PACK CARBURISING

Pack carburization is the oldest method among the case hardening treatments and sufficient attempts has not been made to understand this process in terms of heat and mass transfer, effect of alloying elements, dimensions of the sample, etc. Thus, a two dimensional mathematical model in cylindrical co-ordinate is developed for simulating pack carburization process for chromium bearing steel (a ternary system (Fe-C-Cr)) in this study. Heat and mass balance equations are solved simultaneously where surface temperature of the sample varies with time, but the carbon potential at the surface during the process remains constant. Fully implicit finite volume technique is used to solve the governing equations. A good agreement has been found between the predicted and published data.  
 
It is observed that two dimension analysis gives better description of the process than one dimension. It is found that the effect of second dimension on the craburising process is significant especially in predicting the case depth near the corners of the sample. Neglecting the second dimension in modeling and subsequently analysis of the results on case depth may provide wrong interpretation and thus may affect the operating life of the specimen. Sensitivity analysis shows that as the size of the sample increases the case depth is decreased and thin layer of charcoal packing increases the case depth.


Figure 1. Comparison between computed and published expt. temperature data.


Figure 2. Computed carbon concentration profile within the specimen (high C concn. at the corner is evident). 2D pack carburizing at 1173 K for 6 hours.
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