Abstract
A high-efficiency coal-fired power plant, called an A-USC (Advanced ultra-supercritical) plant, is being developed. In high-temperature sections of the A-USC plant, Ni-base superalloys is one of the possible candidates to replace ferrite steels. On the other hand, renewable energies are being widely promoted, which vary power output depending on those sources. Therefore, the fossil power plants including the A-USC plant are expected to cover the needs of the adjustment of the power supply to satisfy electricity demand. However, it is suggested that the output adjustment would induce fatigue damage in which the oxidation of material interacts. Meanwhile, the dependence on the cyclic loading frequency was investigated to understand the fatigue and creep interaction in a steam environment. Therefore, with aiming to evaluate the dependence of oxidation behavior of Ni-base superalloy, alloy 617, the crack growth behavior in a steam environment at 750°C is evaluated under cyclic loading using a compact tension specimen. It was found that crack propagated along grain boundary under lower cyclic loading frequency. In addition, localized oxide formation was more significant under such condition.
