Development and mechanical property evaluation of Ti, Nb-modified advanced radiation resistant austenitic ($AR^2A$) alloys for reactor internals

Abstract

A set of irradiation resistant austenitic stainless steels were developed utilizing the thermodynamic calculation and thermo-mechanical processing (TMP) for the potential application as nuclear reactor internals materials. The chemical composition was set to have the advantages of phase stability according to the temperature, irradiation and corrosion resistant characteristics. Stepwise heat treatment was performed in order to precipitate fine titanium nitride and niobium carbide at high temperature ($> 850^\circ C$). In the case of TiN, the volume fraction was not so large, but it contributed to grain size refinement by pinning effect. Meanwhile, the volume fraction of fine NbC was large enough to achieve irradiation resistance by providing a large amount of sink sites such as phase boundaries. Cold rolling and re-crystallization heat treatment was carried out to further increase the amount of dislocation and grain boundary which act as sink sites. Finally, the mechanical properties and calculated sink strength were compared in view of the alloy composition and subsequent TMP.