Thermo-mechanical fatigue tests on uniaxial and component-like 1CrMoV rotor steel specimens

An extensive project has been undertaken to characterize the thermal fatigue behaviour of 1CrMoV rotor steel under service-like loading conditions. In the first phase of activity, thermo-mechanical fatigue (TMF) tests were performed on plain uniaxial tensile specimens subject to service-like loading conditions characterized by low strain rates, thermal transients to 565 °C and long hold times at the peak temperature. These were followed by thermo-mechanical fatigue tests performed on circumferentially notched bars in order to study creep–fatigue crack initiation and short crack growth behaviour at stress concentrations. In the final phase of the project a new thermal fatigue experiment was implemented, applying severe thermal cycles to a large 3D feature specimen with a complex 10 mm deep groove. The experiment aimed to reproduce at specific notch locations loading conditions representative of turbine rotor features in service in terms of multiaxial stress state and thermal strain gradients. The results of these TMF and thermal fatigue studies are summarized in this paper.