The effect of the Si content upon bulk and intergranular diffusion in the 16Cr-14wt%Ni austenitic stainless steel was studied by using the residual activity method. The highest intergranular diffusion rate and the lowest activation energy for the component elements of the basic solid solution were found for 1wt%Si. The expressions for the bulk diffusion of 63Ni were:

0.1wt%Si:     D (cm2/s) = 1.7 x 10-1 exp[-272(kJ/g-atom)/RT]

1wt%Si:     D (cm2/s) = 2.3 x 10-1 exp[-272(kJ/g-atom)/RT]

4wt%Si:     D (cm2/s) = 3.4 x 10-1 exp[-272(kJ/g-atom)/RT]

The expressions for the grain-boundary diffusion of 63Ni were:

0.1wt%Si:     D (cm3/s) = 5.18 x 10-8 exp[-174(kJ/g-atom)/RT]

1wt%Si:     D (cm3/s) = 1.21 x 10-8 exp[-159(kJ/g-atom)/RT]

4wt%Si:     D (cm3/s) = 2.0 x 10-4 exp[-257(kJ/g-atom)/RT]

This behavior was explained in terms of a modification, of the interfacial energy, induced by Si segregation.

W.Assassa, P.Guiraldenq: Metal Science, 1978, 12[3], 123-8

Table 96

Bulk and Grain Boundary 63Ni Diffusivities in

Fe-Ni-19wt%Cr Alloys at 900C