TEM CHARACTERIZATION OF DISPERSOIDS AND MICROSTRUCTURE OF ODS-316 AUSTENITIC STEEL

Super-critical water-cooled reactor (SCWR) has been selected to be one of the most potential advanced nuclear reactors due to its simplification and high efficiency. Oxide dispersion strengthened (ODS) austenitic steels are promising candidate materials for SCWR, which combine the advantages of both austenitic stainless steels and ODS steels. In this work, ODS-316 austenitic steel (316L+0.35%Y2O3+0.3%Ti, mass fraction) was fabricated by the process of mechanical alloying (MA) and hot isostatic pressing (HIP). The microstructural evolution after milling and hipping were studied by XRD. Morphologies and electron diffraction patterns of dispersed particles were characterized by TEM. Tensile properties of ODS austenitic steel were measured at room temperature. It was found that there were two phases of alpha (FeCr) and gamma (Fe, Ni) in the powders after mechanical alloying, which was resulted from strain induced transformation. ODS-316 austenitic steel was single austenitic phase, since the strain disappeared during the consolidation of HIP. According to the observation and characterization of TEM, three kinds of dispersoids were found in samples: cubic Y2Ti2O7 and TiN and orthorhombic Y(2)TiQ(5). However, most of the dispersoids were round particles that enriched in Y, Ti and O. The tensile strength of ODS-316 austenitic steel was improved significantly, and its UTS reached 726 MPa.