Mechanism of the drop in the dependence of yield stress on neutron irradiation dose for low-alloy steel

In the present work, influence of irradiation on tensile and impact properties of Cr-Ni-Mo steel using for WWER-1000 type reactor pressure vessel (RPV) manufacturing was studied. An abnormal behavior of tensile properties of the investigated materials under irradiation was observed. Decrease in yield stress and ultimate tensile stress at the first stage of irradiation was revealed while ductile-to-brittle transition temperature (DBTT) was continuously increasing with damage dose. A model of the phenomenon considering influence of residual impurities and alloying elements on α-Fe lattice tetragonality under irradiation was proposed. Some experimental evidences of the model were found. Nickel was supposed to govern the radiation sensitivity of WWER-1000 type steel.