Influence of manganese on the microstructure and mechanical properties of oxide-dispersion-strengthened steels

A novel high-Mn oxide-dispersion-strengthened (ODS) steel, with high cryogenic temperature impact energy, was developed. The effect of Mn content on the microstructure and mechanical properties of ODS steels were examined. The addition of 25 wt.% Mn to ODS steel resulted in transformation from a full ferrite phase to austenite and εhcp-martensite phases. ODS steel without added Mn contained a high number density of fine Y-Ti-O oxide particles. In contrast, ODS steel with 25 wt.% Mn contained TiMn2O4 and relatively coarser Y2Ti2O7 oxide particles with lower number densities. The TiMn2O4 particles showed a crystallographic orientational relationship with the matrix phase. In addition, a high density of deformation twins were formed in tensile-deformed ODS steel with 25 wt.% Mn, but were absent in tensile-deformed ODS steel without added Mn. The ODS steel containing 25 wt.% Mn exhibited higher room-temperature tensile ductility and higher Charpy impact energy at cryogenic temperature without Mn due to the existence of deformation twins, austenite phase, and εhcp-martensite phase in the former.