Fatigue fracture of surface-modified layers in 18CrNiMo7-6 carburized steel

Abstract

A modified layer of a certain thickness is produced on the surface of 18CrNiMo7-6 alloy steel after carburizing and quenching that greatly affects the microstructure and fatigue properties of the material. In this work, the fatigue performance of each layer was studied. The fatigue fracture and tensile fracture were compared under different depths of the modified layer. The fatigue fractures of the modified layer for different stresses were analyzed. As the depth of the modified layer increased, the slope of the S–N curve gradually decreased. As the depth of the modified layer increased, the fracture mode changed from brittle fracture to brittle-ductile mixed fracture, the shear lip became thicker, and the dimple became larger. There was no flat area in the tensile fracture. At the same depth of the modified layer, a smaller stress amplitude, led to a larger proportion of the crack propagation area.