Development and characterization on microstructure and mechanical properties of Zr-alloyed ultra-low-carbon high-Cr ODS steel by Al addition

Al-free-ODS and 4Al-ODS steels were fabricated to investigate the influence of Al addition on the microstructure, tensile and impact properties. The morphology, crystal structures and interface coherency with matrix of nano-oxide particles were characterized. The results show that the number density of nano-oxide particles in 4Al-ODS steel increased from 1.1×10²³ to 1.3×10²³ m^-3, while the average size slightly increased from 8.2 ± 1.6 to 9.3 ± 1.6 nm compared to those in Al-free-ODS steel. Y₂(Zr_0.6Ti_0.4)₂O₇ and additional YAlO₃ nano-oxide particles were found in 4Al-ODS steel with better coherent relationship with the matrix. At room temperature to 1273 K, all tensile test results showed that the strength of 4Al-ODS steel consistently increased without a significant reduction of elongation. The total elongation tested at 973 K was about 49%, which was significantly higher than most of ODS steels in the literature. Although the addition of Al slightly elevated the ductile-to-brittle transition temperature, the upper shelf energy was almost unaffected and remained as about 97.5 J, which is still superior to most of ODS steels as reported.