Influence of high dose neutron irradiation on microstructure of EP-450 ferritic–martensitic steel irradiated in three Russian fast reactors

The microstructure of EP-450 ferritic–martensitic steel was determined after irradiation in BN-350, BN-600 and BR-10 fast reactors at temperatures in the range 275–690 °C. The examinations confirm a high resistance of EP-450 steel to void swelling, but the resistance appears to be lower when the dpa rate is reduced. Depending on irradiation dose and temperature the following was observed: voids (285–520 °C), dislocation loops and linear dislocations (275–520 °C), α′-phase (285–520 °C), χ-phase (460–590 °C), and M2X precipitates (460–690 °C). It appears that the formation of dislocation loops and α′ precipitates at high densities is responsible for the low temperature embrittlement observed in this steel.