Microstructure and Mechanical Properties of Forged High Yttria 18Cr-ODS Steels

摘要

Oxide dispersion strengthened (ODS) ferritic steels are candidate materials for clad tubes in the upcoming Generation IV nuclear reactors. In the present work, a powder forging consolidation technique has been used for fabrication of ODS steels. Two alloys having nominal compositions (in weight %) of Fe-18Cr-2W-0.285Ti-0.5Y(2)O(3) and Fe-18Cr-2W-0.571Ti-1Y(2)O(3), respectively, have been studied in this work. The alloys were prepared by mechanical alloying of elemental powders with yttria in a Simoloyer high energy horizontal attritor. The milled powders were consolidated at 1473 K by powder forging in a flowing hydrogen gas atmosphere. Yttria to titanium ratio was kept constant at similar to 1.75 for both the alloys. TEM micrographs of the forged alloys showed fine recrystallized grains with a dispersion of nano-size Y-Ti-O oxide particles. High-resolution transmission electron microscope fringes and the corresponding fast Fourier transformation confirmed the presence of orthorhombic Y2TiO5 oxide particles in a ferrite matrix. These were the predominant oxide particles in the forged alloys. The Y2TiO5 particles were incoherent with the matrix and exhibited a cuboidal morphology. Despite their high yttria content, both the alloys showed high tensile strength and ductility at room temperature and 973 K. Reasons for this are discussed.