EFFECTS OF AGING CONDITION ON THE HIGH-TEMPERATURE PROPERTIES OF PRECIPITATION HARDENED 15CR-26NI-1.25MO IRON BASE ALLOY

Optimum aging condition suitable to large parts made of low carbone low titanium 15Cr-26Ni-1.25Mo iron-base alloys was examined. The alloys are beneficial to making rotors for ultra-super critical steam turbine for generator. After solution treatment, the alloys were aged at 740°C for 1 through 64h, or 700 to 780°C for 16h. Aging at a range of 720 to 780°C for 16h yielded spheroidal γ′ particles. But, after aging at 780°C for 16h coarsened γ′ particles precipitated on the grain boundary. Superior tensile properties were resulted after aging at 740°C for 16-32h or 740-760°C for 16h. Creep properties at 650°C were affected by aging temperature. The long-term creep strength was hardly affected by the aging temperature in the range of 710 to 760°C for 16h. Creep ductility was significantly improved with elevating aging temperature up to 760°C. Low cycle fatigue strength at 650°C was not affected by the aging conditions when tested under constant total strain amplitude in this work.