The influence of hydrogen on the fatigue behaviour of base and gas tungsten arc welded Eurofer

Room temperature hydrogen embrittlement susceptibility of Eurofer base-metal and gas-tungsten-arc-welded joint has been investigated by fully-reversed load-control low cycle fatigue. The tests were run on specimens subjected to electrochemical charging before and during cyclic stressing. Compared to the uncharged condition, increasing amounts of hydrogen in base-steel caused fatigue life reduction by promoting premature cracking of either grain boundaries or cleavage planes. Examination of fracture morphologies indicated that the underlying embrittlement mechanisms likely correlated with plastic flow alteration and interatomic bond decohesion, both induced by hydrogen. Specimen-to-specimen response variability by test replication was accounted for in terms of Eurofer material heterogeneity, based on relevant experimental indexes. This interpretation was consistent with the well known sensitivity to microstructure of hydrogen embrittlement processes, and explained the large scatter of fatigue lives and failure modes subsequently observed in equivalently charged Eurofer weld samples.