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 irradiate d with 800 MeV protons in the LANSCE facility of the Los Alamos National La boratory (LANL) to a total number of about 6.3 x 10(22) protons (2.8 Ah) in a temperature range from 50 degrees C to 230 degrees C. Tensile tests show that irradiation hardening increases with fluence up to the maximum attain ed dose of about 6.6 dpa. All irradiated specimens show significant embritt lement, less than or equal to 1.5% uniform elongation and 7.5-9% total elon gation as compared to about 11% uniform elongation and 21% total elongation for the unirradiated specimens. SEM observations illustrate that the fract ure of specimens changes gradually from ductile mode in unirradiated and lo w dose specimens to cleavage mode in specimens of high dose (greater than o r equal to 5.6 dpa). Intergranular brittle fracture mode has not been obser ved. Irradiation induced small defect clusters exist in all samples of irra diated 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 greater than or equal to 10 nm have been observed in addition to the cluste rs. (C) 2000 Elsevier Science B.V. All rights reserved.