High strength 12% Cr heat resisting steel for high temperature steam turbine blade

The factors to attain the high creep rupture strength for 12% chromium ferritic steels were studied. Large amount of Laves phase and high content of solute elements during creep were important to maintain the creep resistance, and the degradation correspond to the recovery of matrix. Based on these studies, the chemical composition of 10.5Cr-2.5W-1Co-0.2Re-VMoNbNB steel with large amount of Laves phase and high solute tungsten content was determined for the new blade material. The producibility of this steel were verified with 2 ton ESR ingots which were successfully manufactured by various industrial processes. The mechanical properties of the trial bars were sufficient to be applicable to the blade, especially the creep rupture strength was very higher than that of 11Cr-1Mo-1W-VNbN steel being used. In near future, this new steel will be applied to commercial power plants with steam condition of 593 degrees C or higher as the blade material.