Development of high purity 2.25Cr-Mo-V-Nb N steel for gas turbine disk

Recently, gas turbine inlet temperature has been raised in order to improve thermal efficiency of power plant, The turbine inlet temperature of 1350 d egrees C has already been attained in the newly developed gas turbine. In c ase of the combined cycle power plant, optimization of compressor pressure ratio corresponding to the increase of turbine inlet temperature is require d to improve the thermal efficiency. Development of higher creep strength m aterial for disk, therefore, is needed to actualize higher thermal efficien cy gas turbine, Extensive studies, based on previous experience, by using s everal heats as laboratory scale have been made for the investigation of ef fects of chemistry and heat treatment on mechanical properties. These labor atory studies indicated that the high purity 2.25Cr-Mo-V-Nb-N steel is suit able to the disks required to the advanced type gas turbine. A trial disk h as successfully been manufactured with this steel from 1000 mm dia. electro slag remelting (ESR) ingot. Several evaluation revealed good material prope rties which meet the requirements of advanced type gas turbine disk, especi ally in toughness and aging embrittlement redundant. The manufacture of act ual disks have successfully been performed. They exhibited satisfactory qua lity in creep rupture and roughness.