A FINITE-DIFFERENCE MODEL FOR THE KINETICS OF SENSITIZATION

The model can be applied to alloy systems in which diffusion of one component to and within the grain boundary determines the rate of precipitation in the boundary. An example application to sensitization of austenitic stainless steel is given. The model predicts the Cr profiles in and normal to the grain boundaries and includes the effect of overlap of the Cr profiles along the grain boundary. Because overlap is considered, the model is applicable in the short time range prior to the formation of a uniform Cr level along the boundary as well as at longer times corresponding to conditions for which error function type models available in the literature are applicable. Thus, the model provides an advantage over existing models in that sensitization time can be calculated once the carbide spacing is known. Calculated Cr profiles agree well with experimentally measured profiles and are consistent with the observation that grain boundaries can be sensitized over their entire length or only along segments of their length.