Study of Nanostructure of Ferritic-Martensitic Steel ChS-139 in Initial State and after Fe Ion Irradiation.

The chemical element distributions and the fine structure were studied using atom probe tomography in ChS-139 steel (Fe-12Cr-Nb-Mo-W-V-N-B) after conventional heat treatment (normalizing at 1190°C for 25 s and subsequent tempering at 720°C for 2 h) and after subsequent Fe ion irradiation at room temperature up to the damage doses of 8 and 16 displacements per atom (dpa). A large number of nanosized clusters (~10²³ m⁻³) enriched in chromium, vanadium, nitrogen, and niobium were found throughout the Ch-139 steel after conventional heat treatment. The chemical element distribution in the M₂₃C₆ carbide, Nb₂(C, N) and M₆(C, N) carbonitride phases, pre-precipitates of M₆X carbide phases, and the Cottrell atmosphere were studied. The changes in the cluster composition and sizes resulting from irradiation at room temperature were found. An increase in the cluster sizes upon irradiation was accompanied by a reduction in the concentrations of chromium, vanadium, nitrogen, and niobium. [ABSTRACT FROM AUTHOR]