Complex study of grain boundary segregation in long-term irradiated reactor pressure vessel steels

Abstract

Grain boundary (GB) embrittlement of reactor pressure vessel steel occurs at the long-term operation through the radiation-enhanced segregation of impurities. All the known techniques of studying the GB segregation have their advantages and disadvantages, and complete information can be obtained only through a comprehensive analysis by different methods.In this paper the level of GB segregation in VVER-1000 RPV steels with high nickel content was assessed by combined methods of Auger electron spectroscopy (by the P monolayer coverage and atomic concentration of other elements); atom probe tomography (by the Gibbsian interfacial excess) and fractographic analysis (by the maximum fraction of brittle intergranular fracture).The results obtained by different methods are in good agreement and show that phosphorus GB segregation increases with the increase of fast neutron fluence, GB concentration of Ni and Mn, the bulk concentration of Ni and Mn, and correlates with the fraction of brittle intergranular fracture.