Microstructure, irradiation hardening and embrittlement of 13Cr2MoNbVB ferritic-martensitic steel after neutron irradiation at low temperatures

Tensile mechanical tests and TEM-study of type 13Cr2MoNbVB ferritic-martensitic steel (Russian-made steel EP-450), neutron-irradiated at temperatures in the range 280-350 degrees C up to doses of 85 dpa, have been carried out. At doses of 0.5-25 dpa, the increment of the yield stress in irradiated steel can be fitted by the equation Delta sigma, MPa = 300 x (dose)(0.2). As the dose increases, the yield stress increment reaches a maximum at 30-40 dpa and then begins to decrease. Damage dose and irradiation temperature dependencies of the ductility, upper shelf energy and ductile-to-brittle transition temperature have also been examined. A TEM-analysis revealed dislocation loops, void and alpha'-precipitation in the microstructure of the irradiated steel. At damage doses higher than 40 dpa, a decrease of loop number density and increase of loop size seem to be the main reasons for irradiation softening and ductility improvement in the temperature interval 330-360 degrees C.