Creep crack growth properties for 12CrWCoB rotor steel using circular notched specimens

摘要

Most heat resisting materials in structural components are used under multiaxial stress conditions. It is important to evaluate the effect of multiaxial stress conditions on initiation and growth of creep cracks, when laboratory data are applied to structural components. The creep crack growth test using a circular notched bar (circumferentially cracked round bar) specimen is a simple method to investigate multiaxial stress effects without using complicated test facilities. Creep crack growth tests have been performed using 12CrWCoB turbine rotor steel. In order to investigate the effects of multiaxial stress and specimen size on creep crack growth properties, the tests were conducted for various notch depths and specimen diameters. The circular notched specimens showed brittle crack growth behaviour under multiaxial stress conditions. Creep crack growth rate was characterized in terms of the C parameter. The creep crack growth rate, for the same C value, increased with increase in the initial notch depth, i.e. as the multiaxiality increased. Creep crack growth properties could be predicted by allowing for the decrease of creep ductility under multiaxial conditions.