改良12Cr鋼ロータ材の開発

抄録

Effects of W addition, Ni and C contents on tensile properties, toughness, creep rupture strength and microstructure in 12Cr-Mo-V-Nb-N steel rotor forging were investigated, using specimens with various amounts of W(0 to 1.24wt%), Ni(0.40 to 1.35wt%) and C(0.12 to 0.19wt%). The results are summarized as follows.
(1) Creep rupture strength was remarkably improved without the decreasing of toughness, by the addition of about 1%W with lower C and higher Ni contents.
(2)The improvement of creep rupture strength in advanced 12Cr steel is mainly caused by the depression of dislocation recovery and the formation of sub-grain structure during creep deformation brought from solid-solution strengthening by W addition.
(3)Trial rotor forging was manufactured based on the above basic research work, and it was proved that this forging had improved creep rupture strength and was satisfied enough with the mechanical properties and quality as a turbine rotor forging.
(4) Also in the turbine blade and casing materials, it was proved that the creep rupture strength was remarkably improved by modifying the chemical composition similar to rotor material.
It is expected that the advanced 12Cr steels obtained from the above R&D are applied for rotor, blade and casing in the future 593°C ultra-super critical turbine unit.