Microstructure and mechanical properties of a novel low-activation austenitic steel after thermomechanical processing

This study investigates the microstructural characteristics of a novel low-activation chromium-manganese austenitic steel, Fe-11Cr-27Mn-W-Ti-V-Ta-Y-0.23C, following two processing routes: 20 % cold rolling (CR) and high-temperature thermomechanical treatment (HTMT) involving 50 % hot rolling deformation at 1100°C. HTMT resulted in the elongation of initially equiaxed grains along the rolling direction and their flattening within the rolling plane. The resulting microstructure comprised submicron and micron-sized fragments, predominantly bounded by low-angle misorientations. In contrast to the CR condition, which exhibited a high density of microtwins, the HTMT sample featured thinner, less dense twins and a dislocation density comparable to the quenched state. The temperature dependence of mechanical properties was evaluated from 20 to 700°C. The yield strength after CR was found to be 1.6 to 1.9 times higher than after HTMT across the entire temperature range. The minimum yield strength at 700°C was over 230 MPa for the HTMT condition and over 350 MPa for the CR condition. Conversely, the elongation to failure after HTMT was 1.4 to 2.6 times greater than that after CR. A minimum elongation of 11.8 % was observed for the CR steel at 500 – 600°C, while the HTMT steel exhibited a minimum of 23.6 % at 650°C. The discussion focuses on the influence of thermomechanical processing on the structural state, mechanical properties, the development of dynamic strain aging, and the underlying mechanisms of plastic deformation and fracture across the studied temperature range.

1. The study was funded by a grant of the Russian Science Foundation - Project No. 22-19-00802-P