Effects of size and spacing of uniformly distributed pearlite particles on fatigue crack growth behavior of ferrite-pearlite steels

Fatigue crack growth tests of three ferrite-pearlite steels with different size and spacing of pearlite particles, which were uniformly distributed in the ferrite matrix, were carried out to investigate the effect of microstructure on fatigue crack growth behavior in the Paris regime. The fatigue crack growth rates for the three materials did not coincide with each other, even when the crack growth curves were arranged by the effective stress intensity factor range. From in situ observations, crack tip stress shielding phenomena, such as interlocking and branching, were found on the crack wake, which enhanced fatigue crack growth resistance. A small size and spacing of pearlite particle seemed to induce small but frequent crack deflections, which resulted in crack closure phenomena. On the other hand, the large size of the pearlite particle seemed to induce stress shielding phenomena and, thus, contribute to high crack growth resistance, which was the main reason for the higher fatigue crack growth resistance of the large size and spacing of pearlite particles compared to the small size of pearlite particles.