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. The experimental results are summarized as follows.
1) 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.
2)Superior tensile properties were resulted after aging at 740°C for 16-32h or 740-760°C for 16h.
3) 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.
4) Low cycle fatigue strength at 650°C was not affected by the aging conditions when tested under constant total strain amplitude in this work.
5) A drum with a weight of 4.5t was produced and solutionized and aged at 740°C for 32h. The test pieces were cut from typical four locations of the drum, and creep tested at 650°C. It was confirmed that dispersion of creep strength with respect to the location was negligible.
