Abstract
Recently, gas turbine inlet temperature has been raised in order to improve thermal efficiency of power plant. The turbine inlet temperature of 1350°C has already been attained in the newly developed gas turbine. In case of the combined cycle power plant, optimization of compressor pressure ratio corresponding to the increase of turbine inlet temperature is required to improve the thermal efficiency. Development of higher creep strength material for disk, therefore, is needed to actualize higher thermal efficiency gas turbine. Extensive studies, based on previous experience, by using several heats as laboratory scale have been made for the investigation of effects of chemistry and heat treatment on mechanical properties. These laboratory studies indicated that the high purity 2.25Cr-Mo-V-Nb-N steel is suitable to the disks required to the advanced type gas turbine. A trial disk has successfully been manufactured with this steel from 1000 mm dia. electroslag remelting (ESR) ingot. Several evaluation revealed good material properties which meet the requirements of advanced type gas turbine disk, especially in toughness and aging embrittlement redundant. The manufacture of actual disks have successfully been performed. They exhibited satisfactory quality in creep rupture and toughness.
