Effects of Inclusion Size and Stress Ratio on the Very-High-Cycle Fatigue Behavior of Pearlitic Steel

Abstract The effects of inclusion size and stress ratio (R) on the very-high-cycle fatigue (VHCF) behavior of pearlitic steel were experimentally assessed. The S–N curve under rotating bending loading exhibited a horizontal asymptote shape and a clear fatigue limit. In contrast, the S–N curve under ultrasonic axial loading exhibited a continuously descending shape, and the fatigue limit disappeared at a fatigue life of 107 cycles. The fine granular area (FGA) within nanograins formed in the crack initiation region only for the samples subjected to VHCF at R = -1. All instances of interior crack initiation were caused by the MnS inclusions.