Yoichi Tsuda

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°C or higher as the blade material.

Development of High Strength 12% Cr Ferritic Steel for Turbine Rotor Operating above 600‡C

An advanced 12% chromium ferritic steel has been developed for the high-temperature rotors in improved fossil-fired power plants. The development of this steel is based on the experimental studies of various 12% chromium heat resistant steels. Effects of alloy elements on the creep rupture strength have been investigated and the 10Cr-1.8W-0.7Mo-V-3Co-Nb-B steel was selected to be a hopeful candidate. This revealed the creep rupture strength was higher than that of 10Cr-1Mo-1W-V-Nb rotor steel being used at 593°C. The producibility and properties of the new steel have been verified with the medium size trial forging manufactured from a 20 ton ingot. Although a few technical subjects are remaining, these are expected to be solved with the modification of the manufacturing process. This newly developed high strength 12 % chromium ferritic steel is expected to be applicable to high-temperature rotors operating at 630°C or above, and the significant improvement of thermal efficiencies would be obtained in fossil-fired power plants.