Rotating bending fatigue tests were carried out on specimens of ferrite-pearlitic ductile cast irons (FPDI) with a shot-peening (SP) treatment. Influences of the SP treatment on the fatigue property was investigated experimentally, and the change of an initial residual stress induced by the SP treatment was discussed. As results, the fatigue strength was improved markedly by the SP treatment, but the S-N diagram showed a two-step bending behavior in long life region over 10{sup}7 cycles. The surface hardened layer and the compressive residual stresses were observed more than 300μm from the surface. Sites of the fatigue crack initiation were transferred from the surface to subsurface in the range of longer life region over 7×10{sup}6 cycles region. The initial compressive residual stress was released partially by higher level stress cycling, however, it was almost constant during the lower level stress cycling.
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