Diffusion was measured in the low-alloy (3335 series) ferritic steel (3Ni-0.78Cr-0.65wt%Mn) at 673 to 873K; where a temper embrittlement effect took place. The HIRBS technique was used. The results were compared to previous ones obtained in pure

α-Fe. The Sn diffusivities were higher than that of Fe self-diffusion. The results (table 147) could be described by:

D (m2/s) = 3 x 10-6 exp[-207(kJ/mol)/RT]

All of the impurity diffusion coefficients lay in a narrow band, along the measured temperatures, both in the pure α-Fe structure (large grain size) and in the martensitic-like morphology of the steel. At longer annealing times, the influence of the microstructure was very important; showing the need to use effective bulk diffusion coefficients. The danger of extrapolating data from a pure matrix, instead of measuring diffusion coefficients in real structures, was emphasized.

D.N.Torres, M.J.Iribarren, R.A.Pérez, F.Dyment: Materials Letters, 2006, 60[3], 301-4

Table 148

Diffusion Parameters for Au in Fe40Ni40B20