Abstract
There are strong environmental and economic pressures to increase the thermal efficiency of fossil fuel power stations and this has led to a steady increase in steam temperatures and pressures resulting in world wide plans for ultra super-critical power plants. For example, in order to improve the thermal efficiency of power plant, there has been a strong drive to develop heat resistant steels with excellent creep, high temperature fatigue and thermal fatigue resistant properties as well as superior oxidation and corrosion resistant properties. In this study, the test material was P122 alloy which has been developed for ultra super-critical power plant. To measure fatigue crack growth rate in low DeltaK range, fatigue tests were performed by DeltaK decreasing method at three different microstructures (Base metal, HAZ, Weld metal) regions. Also DeltaK increasing tests were performed to investigate fatigue crack growth rate after DeltaKth values were found at each microstructure. Tests were performed with compact tension specimens at 600700 Delta with the loading frequency of 20Hz. Experimental results of the fatigue crack growth rate in low DeltaK range were analyzed to determine the effect of microstructures at different test temperatures.
Keywords: High temperature, HAZ (Heat Affected Zone), P122, Fatigue, Weldment