It was suggested that the presence of a graded microstructure, such as those found in heat-affected zones, could modify the susceptibility of the material to H-induced cracking. In order to clarify the role that was played by the various microstructures which were present in a heat-affected zone, large simulated zones were produced by using a Gleeble machine and were studied by using the H electrochemical permeation technique. The method was used without a Pd coating, but the surface electrochemical conditions were carefully controlled. It was found that the permeation and out-gassing rates were clearly related to the volume fraction of martensite. In the case of ferrite-pearlite structures, the presence of small AlN and NbC precipitates also had an effect upon the permeation rate.

P.Manolatos, C.Duret-Thual, J.Le Coze, M.Jerome, E.Bollinger: Corrosion Science, 1995, 37[11], 1785-96