The correlation between prior fatigue damage and remaining creep properties in a high chromium steel welded joint

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Strain cycling prior to a constant load exposure is expected to influence the creep properties. The present work aimed to evaluate the effect of prior low cycle fatigue (LCF) damage on the remaining creep properties of P92 steel welded joints. Strain amplitudes of 0.25%, 0.4% and 0.6% and fatigue cycles ranging from 10% to 80% of the number of cycles to failure (Nf) were introduced in creep specimens to represent fatigue damage. A critical analysis of the creep test responses revealed that a high strain amplitude and high fatigue cycles induced a clear reduction in the remaining creep life; conversely, prior LCF also led to a significant increase in the creep rupture strain. It was found that prior LCF loading produced its saturated effect after fatigue cycles at 70% Nf or a strain amplitude of 0.4%. It is important to note that the degradation of the remaining creep life of a welded joint was more severe than that found in homogeneous base metal. It was also observed that the failure location and development of creep voids were dependent on both the number of fatigue cycles and strain amplitude. Additionally, the prior fatigue damage was evaluated using a defined damage parameter that revealed two nonlinear stages of fatigue damage.