Mechanical Alloying and Powder Forging of 18%Cr Oxide Dispersion-Strengthened Steel Produced Using Elemental Powders

Abstract

Oxide dispersion-strengthened (ODS) ferritic steels are potential materials for cladding tubes in fast breeder fission reactors. These are mostly prepared by mechanical alloying of yttria powder with pre-alloyed powders. Using elemental powders offers flexibility in the choice of alloy compositions. Here we report mechanical alloying of Fe-18Cr-2W-0.2Ti-0.35Y2O3 (compositions in wt.%) ODS steel using elemental powders of Fe, Cr, W and Ti with yttria powder. After 5 h of milling, no significant changes in particle size and crystallite size were observed. Powders milled for 5 and 7 h were consolidated through powder forging route. The optimum milling time for mechanical alloying could be determined only after evaluating the forgings. It is difficult to achieve recrystallization in ODS alloys. The forging process parameters were optimized to achieve a dense alloy with a fine recrystallized microstructure. Factors leading to recrystallization are discussed. It is shown that recrystallization in ODS steels is more likely to occur during forging as compared to extrusion/rolling. The powder forging route offers several advantages over the conventional extrusion or HIP routes.