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Superalloys are world-wildly used not only for aerospace but also for chemistry, oil & gas and power engineering application. In recent years the 700 °C level Advanced Ultra-Super-Critical (A-USC) technology with high thermal efficiency is developing in the world to reduce the coal consumption and pollution emissions. Any kind of advanced ferritic and austenitic heat-resisting steels can not meet 700 °C A-USC technology requirement. In this case high quality Ni-base superalloys must be adopted for 700 °C A-USC technology. The research and development of Ni-Fe and Ni-base superalloys such as HR6W, GH2984, Haynes 230, Inconel 617/617B, Nimonic 263, Haynes 282, Inconel 740 and 740H are reviewed in this chapter. wildly used. Recently for further raising thermal efficiency and reduction of CO 2 emission the 700 °C advanced ultra-super-critical (A-USC) power plant development projects are initiated in Europe, United States, Japan, China and India also. In 700 °C A-USC project the highest temperature parts are boiler super-heater and re-heater tube components. The fire-side metal temperature of these components can reach 750-760 °C even higher. Today's modern power plants are required for very long time service such as 30-40 years. There are very strict requirements of these high temperature tube materials such as:1. The high temperature stress rupture strength for 10 5 h should be higher than 100 MPa; 2. The fire-side metal oxidation layer after 10 5 h should be less than 1 mm;3. Good structure stability at long time service and no harmful phase formation; 4.Good process performance such as fabrication and welding ability etc.At above mentioned serious condition any kind of ferritic and austenitic heat-resisting steels can not fulfill these requirements. The high quality Ni-base superalloys must be used for A-USC power plant application. Figure_1 clearly shows the ratio change of high temperature materials with the steam parameters development for coal fired power plants. The Ni-base superalloys will occupy 29% for a 360 bar/700 °C/720 °C A-USC power plant [1].250 bar/540 °C /560 °C 280 bar/600 °C /620 °C 360 bar/700 °C /720 °C

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