Evolution of microstructure and mechanical properties of an oxide dispersion strengthened austenitic steel during aging at 973 K

A 25Ni20Cr oxide dispersion strengthened (ODS) austenitic steel was fabricated by mechanical alloying (MA) and hot isostatic pressing (HIP). The microstructure and mechanical properties stability of the 25Ni20Cr-ODS austenitic steel were investigated thermally aged at 973 K up to 1000 h. Scanning electron microscope (SEM) and transmission electron microscope (TEM) together with tensile and impact tests on the aged material were carried out. As a result, the studied ODS steel shows superior microstructure thermal stability, and dispersed Y2Ti2O7 oxide particles formed in the matrix. The change of dispersed Y2Ti2O7 panicles volume fraction and number density are not obvious after 100 h thermal aging, which leads to no changes in strength and hardness. After aging for 1000 h, a slight reduce in the volume fraction and number density of Y2Ti2O7 particles in the alloy is accompanied by a slight decrease in the UTS. Overall, the tensile properties remain basically stable after thermal aging at 973 K. The UTS remains approximately 707 MPa with an elongation of 27% in the sample after aging for 1000 h. While, the aged material shows a ductile fracture and has a higher impact energy (80 J) after 1000 h aging. According to the results, it indicates that the studied steel provides good stability in microstructure and mechanical properties after long time aging at 973 K.