DEVELOPMENT OF ODS AUSTENITIC STEEL BY MECHANICAL ALLOYING

Abstract

For fast breeder reactors, the structural materials are exposed to high neutron environment mated with high temperature. P/M ODS Austenitic stainless steels have proven to be an adequate material for fast breeder reactor fuel cladding application. The highly stable Y203 particles acts as a barrier to the movement of dislocations and prevent irradiation swelling by working as a trapping site for point defects thereby increasing high temperature strength. The steels strengthened by Oxide dispersion mechanism can enable even higher service temperatures up to 933-1083 K in Sodium cooled Fast Reactor applications. Iron based ODS alloys synthesized by mechanical alloying have been mainly consolidated by hot isostatic pressing (HIP) and hot extrusion. HIP is associated with the problem like residual porosity. Prior particle boundaries and Hot extrusion is associated with anisotropy in mechanical properties. Powder forging is a consolidation technique which is used to produce fully dense material. Powder forging involves the deformation of a powder preform in which considerable lateral flow occurs. The lateral flow of forging leads to considerable shear, which breaks up any oxide surfaces on the particles and enhances bonding between particles. This enhances dynamic properties such as fracture toughness and fatigue strength. In the present work, ODS steel is prepared by elemental powder metallurgy route. The effect of addition of Yttria and the variation in mechanical properties as a result of variation in amount of added yttria is also carried out. The thesis includes six chapters in which Chapter 1 gives the introduction of the ODS steels, mechanical alloying, powder forging and the objective of the report. Chapter 2 discusses literature review about super alloy, alloys used for nuclear industries, mechanical alloying, powder forging and dispersion hardening. Chapter 3 gives the formulation of the problem. Chapter 4 describes the experimental procedure. Chapter 5 details the results obtained and their analysis. Chapter 6 includes Conclusions; Suggestions for future work are given at the end of the thesis and references.