In recent years, advanced ultra-supercritical (A-USC) power plants have developed rapidly to increase the thermal efficiency and decrease CO2 emission. Inconel 740H (IN 740H) is one of the Nibased superalloys with the...
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In recent years, advanced ultra-supercritical (A-USC) power plants have developed rapidly to increase the thermal efficiency and decrease CO2 emission. Inconel 740H (IN 740H) is one of the Nibased superalloys with the highest creep strength and good corrosion resistance at elevated temperatures. Owing to its excellent comprehensive properties, IN 740H is considered one of the best candidate materials for superheater and reheater in A-USC power plants. Further improving the mechanical properties of IN 740H welded joint enhances the safety and economic viability of the power plants. In this study, IN 740H tubes were welded by multipass tungsten inert gas hot-wire welding followed by a post weld heat treatment (PWHT) at 800 degrees C for 5 h. The formation mechanism of the gamma '-denuded zone in the IN 740H welded joint after creep at different temperatures was systematically investigated using OM, SEM, and TEM, and its effect on the mechanical properties was *** show that the small rod-like gamma ' phase only discontinuously precipitates at grain boundaries in the weld metal during PWHT. After creep at different temperatures, an earlier formation of a coarse rod-like gamma ' phase and gamma '-denuded zone is observed at grain boundaries in the weld metal than in the base metal. The formation of the coarse rod-like gamma ' phase at grain boundaries in the base metal results from the discontinuous coarsening of the spherical gamma ' phase near grain boundaries, whereas that in the weld metal results from the discontinuous coarsening of the discontinuously precipitated rod-like gamma ' phase at the grain boundaries and spherical gamma ' phase near the grain boundaries. The discontinuous coarsening of the rod-like gamma ' phase and precipitation of M23C6 carbides at grain boundaries lead to the formation of the gamma '-denuded zone. Increasing the creep temperature and creep time when the temperature is in the range of 700-800 degrees C increases the size of
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