The effect of nanostructured surface layer on the fatigue behaviors of a carbon steel

A nanostructured surface layer was formed on a carbon steel by means of surface mechanical attrition treatment (SMAT). The microstructure of the surface layer of the SMATed sample was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Microhardness and residual stress distribution along the depth from the SMATed surface layer were measured at the same time. Fatigue behaviors of the carbon steel subjected to the SMAT process were investigated. A nanostructured layer with average grains size of ∼12.7 nm was formed, of which microhardness is more than twice as high as that in matrix and residual compressive stress can reach about −400 MPa with maximum depth of ∼600 μm. The fatigue strength of as-received sample is 267 MPa and that of SMATed sample is 302 MPa based on fatigue life 5 × 10⁶ cycles. The SMAT process has improved the fatigue strength by as much as 13.1% for the carbon steel. It is shown that the SMAT is an effective method to render the material with the features, such as a nanostructured and work-hardened surface layer as well as compressive residual stresses, which can pronouncedly improve the fatigue strength of the carbon steel.