Comparison of the low cycle fatigue behaviour of F82H mod. and Eurofer 97 in water coolant

A comparative study has been done about the susceptibility to environmentally induced damage of the reduced activation martensitic steels F82H mod and Eurofer 97. Both alloys were found to suffer premature fracture compared to air behaviour, during conventional fully reversed load controlled low cycle fatigue tests, run in high temperature aqueous environment with the alkaline chemistry specified for the lithium lead blanket water coolant. The different steel low cycle fatigue responses in water, especially, the scatter of fatigue lives and fracture modes observed from plate-to-plate and from specimen-to-specimen in F82H and Eurofer, respectively, appeared to coincide with the presence of different inclusion types, size and density. Based on electrochemical and fractographic indexes, the results were discussed with the support of the hydrogen decohesion model, in terms of mutually competitive trap effects on hydrogen diffusion and partitioning among the susceptible cracking sites.