Correlation between volume fraction of radiation-induced precipitates and toughness of VVER pressure vessel steel 15Kh2MFA

The deterioration of mechanical properties of reactor pressure vessel (RPV) steel during its irradiation in a nuclear power plant is known as neutron embrittlement. It is for instance manifested as a shift of the ductile - brittle transition temperature toward higher values. The microscopic mechnisms of neutron embrittlement of low alloy RPV steel are not yet fully understood. It is known that dislocation loops, vacancy clusters (voids) and precipitates are formed during irradiation.
The dimensions of radiation induced precipitates are less than 5 nm, in RPV steel 15Kh2MFA they are about 1 - 3 nm. One of the objectives of present research in this field is to throw light on the nature of these precipitates.
In this article the correlation between the results of small angle neutron scattering (SANS) and the ductile - brittle transition temperature are studied and possible mechanisms of neutron embrittlement are discussed.