This paper investigates the influence of various hold times on creep-fatigue life at 600oC. The relationship between the crack growth behavior and hold time was studied, and a metallurigical investigation to examine the effect of creep was performed. To examine the relationship between creep-fatigue life and microvoids, the fraction of micro-voids/cavity area was analyzed at the crack tip. The crack growth rate of the HAZ was found to be faster than that of base metal while creep-fatigue life was found to be shorter. Finally, it can be stated that the fraction of cavity area, Fca could be utilized for the life prediction under creep-fatigue interaction. As the hold time increased, the creep damage was observed along the prior austenite grain boundaries and inside and boundaries of delta-ferrite.