Nano-mesoscopic structural control in 9CrODS ferritic/martensitic steels

Effects of varying oxygen concentration and final heat treatment on high-temperature strength and microstructure in 9Cr-oxide dispersion strengthened steel (9CrODS) were investigated. It was shown that appropriate control of excess oxygen concentration remarkably improves creep strength of 9CrODS. This creep strength improvement is ascribed to ultra-fine oxide particle dispersion in a part of the grains and increasing austenite (γ) to ferrite (α) diffusional transformation. Enhancement of austenite (γ) to ferrite (α) diffusional transformation leads to suppression of grain boundary sliding. Creep strength of 9CrODS can be remarkably improved by controlling excess oxygen concentration and performing a furnace-cooling heat treatment for austenite (γ) to ferrite (α) diffusional transformation.