LOW-CYCLE FATIGUE PROPERTIES OF THE HELIUM-IMPLANTED 12-PERCENT CR STEEL 1.4914 (MANET)

Fatigue specimens of the normalized and tempered fully martensitic steel DIN 1.4914 were irradiated at the Dual Beam Facility of KfK. The influence of irradiation temperature (300-600-degrees-C), damage level (0.3-1.2 dpa), helium dose (less-than-or-equal-to 200 appm) and He dose/damage ratio have been studied in strain controlled low cycle fatigue experiments at temperatures equal to the irradiation temperature. All irradiated specimens showed cyclic softening with a slope of the stress amplitude very similar to that of unirradiated ones. In specimens with 200 appm He and 1.2 dpa the stress amplitude at 300-degrees-C is increased by 11% and it is slightly decreased above 450-degrees-C. Under all irradiation conditions only small changes in the number of cycles to failure were observed and the fracture mode is found to remain always ductile and transgranular.