Tensile properties of 9Cr–1Mo martensitic steel irradiated with high energy protons and neutrons

Tensile specimens of 9Cr–1Mo martensitic steel in three metallurgical conditions (tempered, 20% cold-worked and as-quenched) were irradiated in SINQ target-3 with high energy protons and spallation neutrons at temperatures between about 130 and 310 °C to doses between 4 and 12 dpa. Tensile properties were measured mostly at room temperature but a limited number of tests were performed at 250 and 350 °C. Scanning electron microscopy observations of fracture surfaces as well as reduction of area measurements were performed in selected cases. Results of preliminary TEM investigations carried out on 3 mm discs irradiated together with the tensile specimens are also presented. Tensile properties are compared with earlier results on martensitic steels irradiated in spallation conditions as well as with tensile data obtained for the same heat of 9Cr–1Mo steel after irradiation with fission neutrons in the OSIRIS reactor. The as-quenched specimens displayed a fully brittle behaviour and SEM observations revealed an intergranular fracture mode. The irradiated cold-worked and annealed specimens showed large increases in strength as well as drastic reductions in uniform elongation up to a dose of about 10 dpa. The fracture surface appearances remained however ductile. The few specimens irradiated to higher doses (up to 12 dpa) recovered significant ductility, which is presently not understood on the basis of the available preliminary microstructural data.