Thermal stability of the microstructure and microhardness of ferritic-martensitic steel after controlled thermomechanical treatments
摘要
The structural-phase state and microhardness of 12% chromium reduced-activation ferritic-martensitic steel have been investigated after thermomechanical treatments involving deformation in the austenitic region at various temperatures, followed by aging at 700 °C for 100 h. For the three studied deformation temperatures (1100, 1000, and 900 °C), the steel microstructure after aging is qualitatively similar: martensitic laths are located within the former austenite grains, with M23C6 carbide particles along their boundaries and MX carbonitrides inside the structural elements. The former austenite grains do not change in size during aging, while the average width of the martensitic laths increases by a factor of 2.5. The size and volume fraction of the MX particles remain unchanged after aging. However, aging leads to the intense precipitation and growth of M23C6 carbide particles. The steel microstructure after plastic deformation at 1000 °C is the most stable under aging conditions at 700 °C for 100 h. In this structural state, the smallest average sizes of carbide phase particles and a higher dislocation density are observed compared to deformation at other temperatures. These microstructural changes result in a 2–2.5-fold decrease in the steel microhardness values after aging compared to the state after deformation and quenching.