•Artificial defects effectively characterized fatigue strength of Ni-Resist.•Maximum-sized defect in a specimen determines fatigue limit.•Extreme-value statistics efficiently predicts lower-bound of fatigue limit.•Competition between propagation of multiple cracks controls fatigue life. Ductile Ni-resist cast iron with an austenitic matrix structure contains significant casting defects that reduce the fatigue strength. Using specimens with artificial defects of various shapes and sizes, rotating bending and tension–compression fatigue tests were carried out. The maximum-sized defect in a specimen determined the fatigue limit. Therefore, the lower bound of the scatter in the fatigue limit was estimated using the area parameter model in combination with the statistics of extreme values applied to the maximum defect sizes. In contrast, the competition between propagation of multiple cracks from small material defects controlled the fatigue life.