Significant efforts on development of advanced ultra-supercritical (A-USC) fossil fired power plants with steam conditions of 700 ℃ and 30 MPa or higher have been made in recent years. The most important consideration is the development of materials for superheater and reheater tubes with working temperature as high as 760 ℃. During the design and application of these materials, phase stability, creep rupture strength and corrosion performance at 700~760 ℃ should be evaluated. A new type Ni-Cr-W-Fe alloy has been designed for A-USC power plants and the microstructure and mechanical properties of Ni-Cr-W-Fe alloy after long-term aging at 760 ℃ was investigated using OM, SEM, TEM and tensile testing in this work. The fractographs of tensile samples were observed. The results show that the average gain size of specimen after solution-annealing at 1100 ℃ is about 80 μm with twin planes present in the matrix. The major precipitates after aging at 760 ℃ for 16 h are M23C6 and g'. The average particle size and the volume fraction of g' phase are approximately 29 nm and 19%, respectively. The coarsening behavior of g' during long-term aging at 760 ℃ follows Ostwald ripening theory. The solution-annealed Ni-Cr-W-Fe alloy performs excellent ductility at room temperature and the fracture mode of is ductile. The room temperature tensile strengths increase obviously with the decreasing of elongation and reduction of area after aging treatment. The yield strengths at both room and elevated temperatures decrease gradually with the extending aging time at 760 ℃. The tensile ductility at room temperature of Ni-Cr-W-Fe alloy decreases after aging from 1000 to 3000 h, while the elevated temperature ductility varies mildly and keeps at approximately 15%.
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