The creep fatigue crack growth behaviour of P91 steel in as-received and ex-service material conditions has been
examined. The crack growth data was characterized using fracture mechanics parameters ΔK and C*. The results
showed that at high frequency (> 0.01 Hz), the CFCG behaviour tend to that of high cycle fatigue crack growth and
is best correlated with the ΔK parameter whereas at lower frequencies, creep mechanisms have been found to
dominant and best correlated with the C* parameter. The correlation between crack growth rate and C* parameter, 862 N. Ab Razak et al. / Procedia Structural Integrity 2 (2016) 855–862
shows that most of the CFCG tested at 600°C to 625°C fall within the CCG P91 scatter band data for this
temperature range. A linear cumulative rule approach has been used to predict the CFCG experimental result by
considering the frequency effect. The data has been found to be relatively consistent with the prediction lines. An
intergranular fracture surface was observed for all CFCG tests examined with a frequency of less than 0.002
indicating that the fracture process is creep dominant.