Thermomechanical fatigue behaviour and damage mechanisms in a 9% Cr steel: Effect of strain rate

Thermomechanical fatigue (TMF) loading is inevitable during the operation of ultra-supercritical power plants. In the present work, TMF tests are carried out at strain rates of 5 x 10-5/s to 4 x 10-4/s and in-phase (IP) and out-of-phase (OP) to investigate the cyclic deformation and damage mechanisms of P92 steel. The results reveal that the increase in strain rate leads to a significant improvement in fatigue life under both IP-TMF and OP-TMF, in which OP-TMF induces more severe damage to fatigue life than IP-TMF. It was found that the fatigue life reaches a maximum after a strain rate of 1 x 10-4 s-1. It is important to note that the action of dynamic strain ageing (DSA) is strain rate-, fatigue cycle- and phase angle-dependent. It was also demonstrated that the effect of the strain rate on the fatigue life is a combined effect of DSA, fatigue cracks, creep voids and oxidation. Additionally, the predictive abilities of various traditional life prediction methods under various loading conditions are comparatively assessed.

Automated summary

In this study, TMF tests were conducted to investigate the cyclic deformation and damage mechanisms of P92 steel under different strain rates. The results showed that increasing strain rate significantly improved fatigue life, with OP-TMF leading to more severe damage compared to IP-TMF. The presence of dynamic strain ageing (DSA) was found to be dependent on strain rate, fatigue cycle, and phase angle, affecting fatigue life in combination with fatigue cracks, creep voids, and oxidation.