Size Effect on the Fatigue Performance of 18CrNiMo7‐6 Alloy Steel

The size effect on the fatigue performance of 18CrNiMo7-6 alloy steel is investigated. From rotating bending fatigue tests at room temperature, the relationship between the stress amplitude and the number of cycles of specimens with different diameters is obtained. The surface topography, residual stress, and fracture surface of the specimen are measured. The results show that the fatigue strength increases with increasing diameter of the specimen. The fracture of the small specimens tends to be brittle fracture, whereas the fracture of the large specimens is inclined to be ductile fracture. The effects of the surface condition, relative stress gradient (RSG), residual stress, and fatigue crack propagation life on the fatigue performance of the alloy are discussed. The reasons for the size effect are interpreted in terms of the change in the RSG caused by residual stress, the trend of the RSG significantly changes with changing specimen size under different stress levels. The crack propagation life of the large specimens is longer than those of the small specimens.