Fatigue Limit Estimation for Post-Peened Induction-Hardened and Tempered Steel Considering Changes in Surface Properties

Shot peening (SP) and fine particle peening (FPP) were performed as post-treatments on induction-hardened and tempered AISI 4140 steels. Furthermore, the combined effects of surface characteristics including changes in surface morphology, compressive residual stress, and hardness on the fatigue limit were quantitatively examined. The surface characteristics of the prepared specimens were investigated using a laser and stereomicroscope, a micro-Vickers hardness tester, and an X-ray device for residual stress measurements. The rotating bending fatigue properties were also examined. FPP increased the fatigue limit of induction-hardened and tempered steel samples by introducing compressive residual stress and increasing their surface hardness. Conversely, the fatigue limit of the steel treated with SP was lower than that of the electrochemically polished sample owing to the formation of large dents. The fatigue limits of post-peened induction-hardened and tempered steels can be estimated using a modified Goodman diagram considering changes in surface properties.