Comparative analysis of the long-term strength of Russian ferritic-martensitic reactor steels

•Authors studied the structural features of advanced Russian BCC reactor steels.•Authors revealed the features of structure changes in steels after creep tests.•Authors established the reasons for the increase in the time to rupture of the steels.•Russian reactor steels are classified in terms of time to creep failure. The paper presents the results of long-term high-temperature creep tests of Russian reactor steels with ferritic-martensitic structure (the duration of some measurements exceeded 8 years). In the current study, the structural-phase transformations, characteristics of creep and long-term strength at 650 °C, 670 °C, and 700 °C under 60–140 MPa in oxide-free and oxide containing steels were determined. The creep tests were performed on specially designed transverse micro-specimens prepared from fuel elements cladding used in the fast-neutron reactor. The creep velocity of the ferritic-martensitic reactor steels was established to be specified by resistance of lath martensite and ferrite structures to diffusion processes of return and recrystallization. The most heat-resistant oxide-free steel contains the largest amount of refractory elements and carbides. The best heat resistance was observed for the steel hardened with thermal-resistant yttrium-titanium nanooxides. The samples made of this steel demonstrated one order less creep velocity at 700 °C under 100 MPa and 100-fold time to fracture in comparison with the oxide-free reactor steels. [Display omitted]