The steady state creep rate equdtion ofa nickel base superalloy Inconel 718, strengthenedby coherent ordered disc-shaped bct γ11 phaseand coherent spherical fcc γ1 phase precipitates,has been established in the stress and temperatureranges of 620-840 MN m-2 and 853-943K, respecti-vely. Constant stress tensile creep tests wereused to medsure the values of steady state creeprate, εs, and the consecutive stress reductionmethod was used to measure the back stress duringcreep deformation. The values of effective stressexponent, ne, were detemined from the slopesof the lgεs vs. lg（σa-σ0）/G plots. The effectof grain size, d, on steady state creep rdtehas been also studied in this investigation,and the grain size sensitive exponents m weredetemined from the slopes of lgεs vs. lg（b/d）plots. The creep rate equations of Inconel 718,in the above stress and temperature ranges,have been proposed to beεs=1.6×10-5（D1Gb/KT） （b/d ）0.19[（σa-σ0）/G]1.35in diffusional creep region, andεs =75（D1Gb/KT） （b/d）-0.42[（σa-σ0）/G]5.5in dislocation power law creep region.
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