The microstructure and mechanical properties of micro-scale Y2O3 strengthened 9Cr steel fabricated by vacuum casting

Casting process is not a common method in producing oxide dispersion strengthened (ODS) alloys due to its difficulty in distributing the oxides in matrix, especially for nano-scale oxide particles. In this paper, 9Cr steel strengthened by micro-scale 0.4 wt% Y2O3 was fabricated through vacuum casting technology containing electromagnetic stirring. Microstructural observation and energy dispersive spectrometry (EDS) analysis of the particles from tensile fracture dimples and extraction by dissolving metal elements, demonstrated that complicated oxides, several microns in diameter, containing elemental Y and O formed and evenly distributed in the steel matrix. The tensile strength was also improved after Y2O3 addition for the steels in both forged and heat treated states, the alloy matrix strengthened was due to the complicated oxides with Y element played a role as obstacles to dislocation gliding. The research confirmed that micro-scale Y2O3 was effectively added to the steel matrix during casting, which provided an alternative method for ODS alloy fabrication.