Dependence of re-embrittlement rate after annealing on the copper, nickel and phosphorus contents in model alloys

Irradiation embrittlement rate as well as the re-embrittlement rate after annealing of pressure vessel steels can in general be described by the copper, phosphorus and nickel contents of the materials. In the current study embrittlement and re-embrittlement rate of 32 different model alloys were measured using sub-size CH-V specimens of dimensions 3 × 4 × 27 mm. The impurity and alloy elements of the model alloys were varied within the limits Cu: 0−1.0 wt-%, P = 0−0.040 wt-% and Ni: 0−2.0 wt-% relatively evenly. The specimens were originally irradiated in the high flux reactor in Petten into a neutron fluence of 0.3×1019n/cm2, E >1 MeV and re-irradiated after the annealing treatment in the Loviisa power reactor into a fluence of 1.0 × 1019n/cm2, E > 1 MeV. In the paper the irradiation and re-irradiation embrittlement rate has been modeled based on the Cu, P and Ni contents of the alloys. Re-irradiation rate was found to be clearly lower than the original irradiation rate except for small corner in the element space, i.e., no nickel, low copper and high phosphorus alloys. Phosphorus coefficient in the re-irradiation shift function is relatively two times higher than in the original irradiation shift function. Many of the alloys in the IAI-condition show intergranular type fracture (IGF). However, the effect of the change of the fracture mode from cleavage to IGF on transition temperature shift remains open. The dependence of irradiation embrittlement, annealing and re-embrittlement behavior on the copper, phosphorus and nickel contents is still not solved, one reason being the relatively limited variation of the key elements in the materials. Model alloys offer a good variation matrix of the elements even, if the measured data cannot be directly applied to real steels