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 As diffusivities were higher than that of Fe self-diffusion. The results (table 145) could be described by:

D (m2/s) = 5 x 10-6 exp[-202(kJ/mol)/RT]

The impurity diffusion coefficients tended to lie 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. The HIRBS technique revealed the true bulk diffusion coefficients in these matrices and the influence upon the diffusivity of the added element. 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 146

Bulk Diffusivities of Sb in 3335 Steel