Tensile properties and microstructure of martensitic steel DIN 1.4926 after 800 MeV proton irradiation

A double-wall window of martensitic steel DIN 1.4926 (11% Cr) was irradiated with 800 MeV protons in the LANSCE facility of the Los Alamos National Laboratory (LANL) to a total number of about 6.3 × 10 22 protons (2.8 Ah) in a temperature range from 50°C to 230°C. Tensile tests show that irradiation hardening increases with fluence up to the maximum attained dose of about 6.6 dpa. All irradiated specimens show significant embrittlement, ≤ 1.5% uniform elongation and 7.5-9% total elongation as compared to about 11% uniform elongation and 21% total elongation for the unirradiated specimens. SEM observations illustrate that the fracture of specimens changes gradually from ductile mode in unirradiated and low dose specimens to cleavage mode in specimens of high dose (≥ 5.6 dpa). Intergranular brittle fracture mode has not been observed. Irradiation induced small defect clusters exist in all samples of irradiated material. Both of the size and the density of clusters increase with fluence. At the highest dose of 6.6 dpa large dislocation loops of a size > 10 nm have been observed in addition to the clusters.