BSTRACTA gradient nanostructured (GNS) surface layer was generated on an ultrahigh strength bearing steel (AISI 52100) by surface mechanical rolling treatment (SMRT). The initial martensite plates with cementite and retained austenite were transformed into nanograined martensite with a mean size of ∼24 nm at the topmost surface. Axial tension–compression fatigue tests showed that an enhanced fatigue property was achieved on the GNS sample due to the suppressed fatigue crack initiation at the surface. Effects from hardness

microstructure

and residual stress in the GNS surface layer were discussed in relation with the fatigue mechanism of the SMRT sample.