大型地熱蒸気タービン用ロータ材料の開発と実用化

摘要

近年，再生可能エネルギーのひとつとして地熱発電が注目されており，地熱発電用蒸気タービンの単体出力や機器サイズも増大しつつある。東芝は，株式会社日本製鋼所と連携して，最大重量が50トン級の大型地熱蒸気タービンロータ用素材に適用できる，優れた焼入性，強度・靭性，耐応力腐食割れ（SCC)性を持ち，かつ鋼塊中心部のC(カーボン)偏析を低減できる材料を開発した。8トン砂型鋼塊の試作により製造性を検証した後，開発材料を実機に適用して，地熱発電所数プラント向けの大型地熱蒸気タービンロータを製造することに成功した。%In recent years, geothermal power generation has been attracting attention as a renewable energy resource, and demand has arisen for increases in the size and output of individual geothermal steam turbine units accompanying the expansion of large-scale geothermal power plants. Toshiba has cooperated with The Japan Steel Works, Ltd. in developing a new material applied for large-scale geothermal steam turbine rotor shafts with a maximum weight in the 50-ton class. This material has the properties of excellent hardenability, satisfied strength & toughness, high stress corrosion cracking resistance, and less center segregation of carbon in the steel ingots. We have verified the manufacturability of the newly developed material in the form of an 8-ton sand mold ingot, and successfully applied it to the manufacturing of large-scale geothermal steam turbine rotor shafts for several geothermal power plants.