Abstract
Advanced 700°C-class steam turbines require the use of austenitic alloys instead of conventional ferritic 12Cr steels, which are inadequate in creep strength and oxidation resistance above 650°C. While austenitic alloys offer improved performance, they traditionally possess a significantly higher coefficient of thermal expansion (CTE) compared to 12% Cr steels. Through extensive research, the authors systematically investigated the effects of various alloying elements on thermal expansion and high-temperature strength. As a result of these investigations, they developed "LTES700," an innovative nickel-based superalloy specifically designed for steam turbine bolts and blades. This novel alloy uniquely combines a coefficient of thermal expansion comparable to 12Cr steels with high-temperature strength equivalent to conventional superalloys like Refractaloy 26, effectively addressing the critical limitations of previous materials.
