Influence of case-carburizing and micro-defect on competing failure behaviors of Ni–Cr–W steel under gigacycle fatigue

• The interior failure becomes the predominant failure mode in the life regime beyond 105 cycles.
• The case-carburizing has no effect on the fatigue strength with interior failure.
• The evaluated defect size is the largest by Gumbel, the second by GP and the least by Weibull.
• The modeling method of S–N curve with the maximum defect size at a given probability is acceptable.

Axial loading test was performed to investigate the influence of case-carburizing and micro-defect on competing failure behaviors of Ni–Cr–W Steel under gigacycle fatigue. The interior failures induced from inclusion and microstructural inhomogeneity become the predominant failure mode in the life regime beyond 105 cycles. The case-carburizing has no effect on the fatigue strength with interior failure. Compared with the lower limit values of experimental S–N data, the predicted results by using GP distribution is relatively suitable. From the viewpoint of reliability, the modeling method of interior S–N curve with the maximum defect size at a given probability is satisfactory.