Microstructure and mechanical properties of Y-modified low-activation austenitic steel

The microstructure characteristics of a new Y-modified low-activation austenitic steel Fe-11Cr-27Mn-W-Ti-V-Ta-Y-0.23C in quenched and cold-rolled states are studied by transmission and scanning electron microscopy. It is shown that dispersed particles of MC (M — Ti, V, Ta) and M23C6 (M — Cr, Mn, Fe) carbides are observed in the steel, which is characteristic of dispersion-strengthened chromium-manganese austenitic steels. Relatively low (26.4 mJ / m2) stacking fault energy favors the formation of increased density of microtwins. It is shown that the limited contents of carbon and strong carbide-forming elements in the composition of the new steel lead to a decrease in the size and number of dispersed carbide particles in comparison with the earlier investigated low-activation austenitic steels. Microadditions of Y contribute to the reduction of the average grain size to 30.6 and 17.7 μm after quenching and cold rolling, respectively. The mechanical properties of the steel are investigated under tensile tests at 20, 650 and 700°C. Some degradation of the strength properties of the new steel in comparison with the known low-activation austenitic steels is accounted for by lower efficiency of dispersion strengthening with carbide particles and solid solution strengthening mainly by reducing the carbon content. The peculiarities of plastic deformation and fracture of this steel after tensile tests are studied. It is shown that at all investigated tensile test temperatures the observed fracture is mainly ductile dimpled transcrystalline fracture. At 20°C, the elements of ductile intergranular fracture are found.