Rationalization and extrapolation of creep and creep fracture data for Grade 91 steel

摘要

New relationships are shown to allow straightforward rationalization and extended extrapolation of multi-batch creep data sets for Grade 91 steel (9Cr- IMoVNb). Specifically, after normalizing the applied stress through the appropriate UTS value, creep property measurements at different temperatures are superimposed onto sigmoidal 'master curves' using the activation energy for lattice diffusion in the alloy steel matrix (300 kJ mol~(-1)). In contrast to currently-adopted analysis procedures, applying the new methodology to results from tests lasting less than 30,000 h allows the minimum creep rates, the times to various creep strains and the creep lives to be predicted accurately for stress-temperature conditions causing failure in times approaching or even exceeding 100,000 h.