A study was made of the effect of thermo-mechanical treatment upon the effusion of H from a thermally-charged free-cutting steel (0.09C, 1.1Mn). The results indicated that a balance existed between void formation and elimination; depending upon the working process and the temperature. The apparent diffusivity of H was related to the overall micro-void volume, as influenced by the presence of gas and shrinkage pores, micro-cracks with inclusions, spherical pores at inclusion/matrix interfaces, and micro-cracks in the matrix. The activation energy for the effusion process was estimated to be between 8.7 and 9.4kcal/g-atom, regardless of the nature of the predominant type of micro-void which was present.

G.M.Evans, E.C.Rollason: Journal of the Iron and Steel Institute, 1969, 207[12], 1591-8