Mechanical long-term properties of nickel-base alloys for steam turbine bolting. Final report.

摘要

Within the reported project three heat resistant nickel-base alloys, Alloy 70 (NiCr 20 Fe 25 TiAl), Alloy 80A (NiCr 20 TiAl) and Alloy X-750 (NiCr 15 TiAl) were investigated for the application to steam turbine bolting in the temperature range of 450 to 600deg C. Important mechanical long-term properties as creep-rupture strength, relaxations strength and contraction were determined to improve the basis for the optimum selection of bolting materials. On the optimized condition of the three materials, some important interdependencies between different mechanical properties were investigated. Using creep and contraction data, it was possible to predict the time-dependent residual stress of the continuous relaxation test with sufficient accuracy. An inelastic finite element calculation of notched specimens of Alloy 80A for 550deg C short-term creep-rupture tests showed, that even under elastoplastic loading there is a risk to crack initiation in the vicinity of the notch. (orig./RHM) With 17 figs., 15 tabs. (ERA citation 16:014903)