Characterization of the nature and morphology of coarse precipitation in various oxide dispersion strengthened steels

Abstract

Abstract Oxide Dispersion Strengthened (ODS) steels are candidate materials for both fission and fusion nuclear reactors. In this study, the microstructure of ferritic (Fe-14Cr-1W) and ferritic / martensitic (Fe-9Cr-1W) ODS steels has been characterized after two different processing routes: Hot Extrusion (HE) and Hot Isostatic Pressing (HIP). Transmission Kikuchi Diffraction (TKD) revealed the presence of Ti-rich precipitates on every specimen. They are identified by X-Ray Diffraction (XRD) as Ti(C,N) and Ti-O (Ti2O3 or TiO2). Intergranular M7C3 and M23C6 have been observed on most Fe-14Cr ODS steels except one, where no Cr-carbides have been found. In Fe-9Cr ODS, intergranular Cr-rich M23C6 carbides have been found. The lack of M7C3 on Fe-9Cr ODS is possibly linked to the matrix phase transformation, not occurring in the Fe-14Cr ODS. Cr-carbides display highly elongated shapes for the Fe-14Cr HE specimens that could be detrimental to the mechanical behavior of the material.