HIRBS measurements of As, Sb and Sn diffusion in a low-alloyed ferritic steel

As, Sb and Sn diffusion was measured in a low-alloyed ferritic steel (3335 series) in the temperature range 673–873 K, where the well-known temper embrittlement effect takes place. HIRBS technique was employed. The results were compared to the previous ones obtained in pure α-Fe. As, Sb and Sn diffusivities are higher than Fe self-diffusion. As shows the higher diffusivity values in the steel while Sn is the fastest one in pure α-Fe. All the impurities diffusion coefficients 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. Only As in steel deviates notably. HIRBS technique lets us determine the true bulk diffusion coefficients in these matrices and, therefore, its influence on the diffusivity of the different elements. For longer annealing times, as it is the case in real service, the influence of the microstructure is very important, showing the need of using the effective bulk diffusion coefficients. The danger of extrapolating data from the pure matrix instead of measuring the diffusion coefficients in real structures is emphasized.