Phenomenological aspects of fatigue cracking in as-received and hardened F82H modified steel exposed to lithiated water with dissolved hydrogen at 240°C

The low cycle fatigue (LCF) behaviour of F82H modified steel with three different degrees of hardness produced by specific thermal treatments has been investigated at 240°C under load control, in oxygen-free lithiated solutions containing either no or 2 ppm dissolved hydrogen. In all cases, it was found that the aqueous environments reduced the fatigue life of the material and promoted fracture modes different from those observed in air tests; the fracture modes comprised intergranular and transgranular quasi-cleavage separations as well as microvoid coalescence, which depended on material conditions and water chemistry. All these features were ascribed to a hydrogen-assisted-cracking (HAC) phenomenon, as the basic mechanism for controlling the fatigue behaviour of various F82H heats in lithiated solutions. The observed differences in HAC paths are discussed from the standpoint of material microstructural and substructural parameters.