Post extrusion heat treatment effects on microstructure and mechanical properties of 9Cr nano structured ferritic alloy

Nano structured ferritic alloys (NFAs) show enhanced high temperature strength by adding nano scale oxide particles into ferritic-martensitic (FM) steel. High Cr FM steels are under intense research as candidate materials for the components of next generation nuclear systems. The adequate mechanical and fract ural properties are prerequisites for core materials that are subjected to a rigorous environment at a high temperature of up to 650 .deg. C and neutron irradiation of 200 ∼ 400 dpa. A few recent researches have reported that the fracture toughness of NFAs is very low at above 300 .deg. C. To overcome this drawback of NFAs, post extrusion heat treatments that can evolve the partial phase transformations in a 9Cr-NFA were applied in this study. The objectives of this study are to improve the fracture toughness and ductility of NFA through a simple post-extrusion thermo-mechanical process, which can lead to changes in the microstructure of nano structured 9Cr alloy into a dual phase structure