To investigate the effect of residual stress on the fatigue crack propagation of 18CrNiMo7-6 alloy steel, the fatigue crack propagation tests were conducted under different residual stress levels and stress ratios, and the fracture surface was characterized using three-dimensional profilometry and scanning electron microscopy. The experimental results indicated that the Paris formula material exponent \(m\) was nearly constant, while the material exponent \(C\) decreased with increasing stress ratio and decreasing residual stress (absolute value increase). Along the crack propagation direction, the surface roughness and fatigue striation spacing gradually increased from the crack initiation region to the final fracture region. As the residual stress decreased (absolute value increased), the fatigue crack growth rate tended to decrease, while the fracture surface roughness increased and the fatigue striation spacing became smaller, which suggested that residual stress could effectively retard crack propagation but its inhibitory effect was significantly weakened under high stress ratio. These findings provided insight into the combined influence of residual stress and stress ratio on fatigue crack propagation, offering guidance for fatigue life prediction and structural design of high-load components.
