Abstract
Diffusion coefficients, D, pertaining to hydrogen evolution from decarburized mild-steel specimens in two conditions of large and small grain size are reported. These were measured to investigate the possibility that grain boundaries alone are responsible for the anomalously low D values found below ∼ 200° C in non-steady-state diffusion work. However, there were no significant differences in the coefficients obtained over the temperature range 25–200° C for the two specimens. All the results lay close to values given in the literature for α-iron,which are all significantly below the values predicted by extrapolation from higher temperatures. Thus, the so-called ‘trapping phenomenon’ was present to the same extent in all the measurements, irrespective of a change in the total grain-boundary area of between one and two orders of magnitude.
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