For sustainable and reliable energy supply sources, advanced thermal power plants (A-USC) is receiving more attention since shutdown of nuclear power plants by an unprecedented devastating earthquake in Japan. For A-USC in reality, new materials with superior long-term creep rupture strength longer than 105 hours under 100 MPa at 973 K are desired. Besides some Ni base alloys, none of the conventional austenitic heat resistant steels meet this requirement. Why? This is due to microstructure instability of major strengthening spices/metallic carbides during high temperature exposure. We have developed novel austenitic steels strengthened by two intermetallic phases of GCP (geometrically close-packed) and TCP (topologically close-packed), and revealed excellent creep performance. In this talk, the design approaches based on phase diagram calculation and new strengthening mechanism called “Grain-boundary precipitation strengthening” by TCP Laves phase is presented. Part of this study was carried under the research activities of the Consortium, financially supported by NEDO.
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