Fatigue crack growth behavior in ferritic–pearlitic steels with networked and distributed pearlite structures

Effect of pearlite morphology on fatigue crack growth behavior in ferritic–pearlitic steels was investigated. Networked-like and distributed pearlite structures were prepared. ΔK decreasing/increasing and constant-ΔK fatigue crack growth tests have been performed inside an SEM chamber. The results revealed that distributed pearlite structure had better fatigue crack growth resistance than networked-like pearlite structure. Grain size and yield strength are the main factors controlling threshold value of the steels. In-situ observation revealed that the distributed pearlite structure indicated tortuous crack path. This tortuous path contributed to crack interlocking as well as crack closure. It was observed that ferritic–pearlitic steel with distributed pearlite structure inhibited the extent of plastic deformation around the crack compared to that in the networked-like pearlite structure. Plastic zone size estimation by using their cyclic stress–strain curves showed that the plastic zone size in distributed pearlite structure was smaller than that in the networked-like pearlite structure.