Effect of annealing temperature on the evolution of microstructure, texture, and mechanical properties of hot-rolled 12Cr-ODS steel

To achieve high thermal efficiency, today's nuclear reactor structures are exposed to higher temperatures and pressures, which requires the use of high-strength steels with specific properties, such as ODS steels. There is a need to clarify the evolution of the microstructure and properties of steels at elevated temperatures. This study systematically investigates the evolution of microstructure, texture, and mechanical property variations of 12CrODS steels after hot-rolling and subsequent annealing at 1000 degrees C and 1200 degrees C. The investigation utilizes optical microscopy, electron backscatter diffraction technique, and mechanical property measurements. The microstructure of hot-rolled samples shows a layered alternating distribution, which is distinguished by a notable presence of the alpha-fiber texture. Following annealing at 1000 degrees C, the martensite grains are smaller with a reduced hardness, while maintaining a strong alpha-fiber texture. After annealing at 1200 degrees C, there is a rapid increase in the growth of martensite grains, a significant rise in hardness, a reduction in the alpha-fiber texture characteristics, and an improvement in the gamma-fiber texture characteristics. Moreover, the maximum intensity of the alpha-fiber texture diminishes as the annealing temperature increases. The mechanical properties of the samples deteriorated after annealing at 1200 degrees C, which can be attributed to the coarse martensite grains and the texture components containing the {001} cleavage plane dominating the occurrence of brittle cleavage fracture. The 0.1Y sample after annealing at 1000 degrees C exhibits an excellent combination of strength (1458 MPa) and ductility (20.3%), which is owing to the unique heterogeneous grain structure and the evolution of favorable texture.