Study on the Evaluation of Fatigue Limit and Harmless Crack Size of Double Shot Peening Treated Carburized Steel

To prevent the reduction of fatigue strength in carburized products due to a sudden temperature increase, the surface characteristics and fatigue limits of specimens that underwent double shot peening (DSP) after tempering at 573 K were evaluated, as well as those of specimens that were tempered at 573 K after DSP. Additionally, the harmless crack size was derived using the compressive residual stresses by DSP. The surface hardness of the specimens by DSP after tempering at 573 K was 31~40 HV higher than that of the specimens tempered at 573 K after DSP. The maximum compressive residual stress of the specimens tempered at 573 K after DSP was 542 MPa lower than that of the specimens by DSP after tempering at 573 K. The fatigue limit of the specimens by DSP after tempering at 573 K was improved by 30% compared to those tempered at 573 K after DSP. The harmless crack size could evaluated using residual stress, fatigue limit and threshold stress intensity factor.