Effect of high dose/high temperature irradiation on the microstructure of heat resistant 11Cr ferritic/martensitic steels

Characterization of microstructure and property evolution in advanced cladding and duct: Materials exposed to high dose and elevated temperature

“…It is observed that for 7 dpa at 500°C, both the average size of the PAGB precipitates and the grain boundary coverage increased compared to 7 dpa at 400°C. Precipitate growth and increased boundary coverage upon irradiation at high doses and temperature close to 500°C has been reported in PNC-FMS steel 58 suggesting that irradiation enhanced the growth of precipitates due to irradiation-assisted diffusion. EDS maps from secondary phases on a carbon extraction replica taken from alloy T91 irradiated at 400°C for 7 dpa clearly indicate coexistence of Cr, Fe, Mo in the larger M 23 C 6 .…”

Characterisation of nano-scale precipitates in BOR60 irradiated T91 steel using atom probe tomography

“…The pre-existing carbides and nitrides contribute to strengthen the material and are expected to be stable under service conditions. However, research has shown that modification of structure, density, size and composition of pre-existing precipitates can occur when exposed to irradiation [8][9][10]. M23C6 was previously shown to increase in size and grain boudary coverage in an 11Cr F/M steel after neutron irradiation at temperatures between 500 o C -650 o C [10].…”

Mechanical properties and microstructural stability of 11Cr-ferritic/martensitic steel cladding under irradiation

“…As described previously, the tensile and transient burst strengths of PNC-FMS claddings degraded due to neutron irradiation at high temperatures, and it was suggested that such significant strength degradation was related to a drastic microstructural change during irradiation, especially recovery of martensite lath structures and precipitation behavior [16][17][18]. However it was still not clarified why in-reactor creep rupture behavior was similar to out-reactor creep behavior at 943 K. Among possible explanations, it is considered that thermal aging rather than neutron irradiation would affect the degradation of in-reactor creep rupture strength, namely the contribution of point defects introduced during neutron irradiation could be negligible because of their rapid annihilation at high temperatures.…”

“…The microstructural observation of PNC-FMS cladding lot 61FS after neutron irradiation in a previous work by Yamashita et al [18] showed the following results. When the specimens were irradiated at low irradiation temperatures between 673 and 723 K to doses up to 94.6 dpa, both dislocation loops and cavities (less than 30 nm in diameter) were formed in the region of the ferrite phase and estimated void swelling was 0.05% at the most.…”