Abstract
Recently advanced ultra-super critical (A-USC) pressure power plants with 700°C class steam parameters have been under development worldwide. Japanese material R&D program for A- USC beside the plant R&D program started in 2008, launched in 2007 under the METI/NEDO foundation includes not only alloy design explores and novel ideas for developing new steels and alloys that can fill critical needs in building 700°C class advanced power plants, but also fundamental studies on creep strength and degradation assessment, which are absolutely needed to assure the long-term safe use of newly developed steels and alloys at critical temperature conditions, for instance, 650°C for ferritic steels, 700°C for austenitic steels and 750°C for Ni- based alloys. This program concept has been based on the lessons from materials issues recently experienced in the creep strength enhanced ferritic steels used for 600°C class ultra-super critical power plants. Particular outputs from the program up to now are recognized as the ferritic steel having the creep strength of 100MPa at 650°C beyond 30,000h without any Type IV degradation and as the austenitic steel developed by means of inter-metallic compounds precipitation strengthening of grain boundary which should be strongest in creep ever found. Concurrently great progresses have been seen in the research works with positron annihilation life monitoring method applicable to various kinds of defects, structural free energy values, small punch creep test data for very limited interest area, crystallographic analyses, optimum time-temperature parameter regional creep rupture curve fitting method, hardness model, etc. which would highly contribute to find out and establish the structural parameters affecting to creep strength and degradation resulting in accurately estimating the 100,000h creep strength.
