Abstract
The commercialization of a 700℃ class pulverized coal power system, advanced ultra-supercritical (A-USC) pressure power generation, is the target of an ongoing research project in Japan. In the A-USC boiler, Ni or Ni-Fe base alloys are used for high-temperature parts at 650-700℃, and advanced high-Cr ferritic steels are planned to be used at temperatures lower than 650℃. In the dissimilar welds between Ni base alloys and high-Cr ferritic steels, Type-IV failure in the heat-affected zone is a concern. The high B-9Cr steel developed at the National Institute for Materials Science, which has improved creep strength in both base metal and weldment, is a candidate material for the Japanese A-USC boiler. In the present study, long-term creep tests were conducted on the dissimilar welded joints between Ni base alloys and high B-9Cr steels. Microstructures and creep damage in the dissimilar welded joints were investigated. The creep rupture life of the dissimilar welded joints using high B-9Cr steel was 5-10 times longer than that of the conventional 9Cr steel welded joints at 650℃. The effect of welding procedure was also investigated.
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