Development of 9Cr-ODS Martensitic Steel Claddings for Fuel Pins by means of Ferrite to Austenite Phase Transformation

Abstract

For use as fuel cladding of liquid metal fast reactors, Fe-0.12C-9Cr-2W ODS martensitic steel claddings were developed by cold-rolling under the softened ferrite phase induced by slow cooling from austenite phase, subsequently by ferrite to austenite phase transformation to break up substantially elongated grains produced by cold-rolling at the final heat-treatment. The produced claddings showed noticeable improvement in tensile and creep rupture strength that are considerably superior to PNC-FMS and even austenitic PNC316 at higher temperature and extended time to rupture. The strength improvement is mainly attributed to titanium addition in ODS martensitic steels through its reduction of Y₂O₃ particle size and shortening inter-particles spacing. The behavior of oxide particle size reduction is associated with stoichiometry between Y₂O₃ and TiO₂.

KEYWORDS:

• oxide-dispersion-strengthened steel
• yttrium oxides
• ferrite
• austenite
• phase transformation
• martensitic steel
• cladding
• tensile strength
• creep rupture strength
• cold rolling
• fast reactors