Effect of thermo-mechanical treatment on short-term mechanical properties of low-carbon 9% Cr martensitic steel

The low-carbon 9% Cr martensitic steel with Co, Cu and Ta doping was thermo-mechanically treated using normalizing at 1200°C for 24 h, interim medium-temperature forging with various strains, following annealing at 650°C with different durations and final tempering at 750°C for 3 h with aim to provide the formation of the stable Z-phase particles instead of the non-equilibrium MN nitrides. Conventional heat treatment consisting of normalizing at 1200°C with following tempering at 750°C was also carried out and provided the formation of the non-equilibrium MN nitrides. The stable Z-phase particles were precipitated after forging with strain higher than 30% and annealing at 650°C during 300 h. The tensile, hardness, and impact toughness tests after thermo-mechanical treatment and conventional heat treatment were carried out at room temperature. The thermo-mechanical treatment provided an insignificant increase in the tensile strength (both yield strength and ultimate tensile strength) and hardness, wherein the plasticity properties (elongation, reduction in area and impact toughness) also retained the good level.