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PurposeThe study aims to examine the effect of inclusions and inherent microstructure on fatigue behavior of 34Cr2Ni2Mo steel.Design/methodology/approachFatigue behavior of 34Cr2Ni2Mo steel was investigated for up to 1E10 cycles.FindingsResults showed that both inclusion and inherent microstructure have an influence on the crack initiation mechanism. Fatigue cracks mostly initiated from inclusions, whereas substrate-induced crack initiations were also observed. Fatigue life of inclusion-induced failures is mostly determined by the location of inclusions rather than the loading stress. The inherent microstructure seems to tolerate inclusions at a lower stress level in very high-cycle regime owing to the absence of internal inclusion-induced failure. For the substrate-induced crack initiations, high-density dislocations are found to be accumulated around the carbide particle-matrix interface, which may be the cause of crack initiation in the inherent structure due to strain localization.Originality/valueThe effect of inclusions and inherent microstructure on fatigue behavior of 34Cr2Ni2Mo steel up to 1E10 cycles.HighlightsFatigue failure occurs even at a lifetime of 5.76E9 cycles.Surface inclusion induced premature failures.Inherent microstructure tolerates inclusions at lower stress level.Internal carbides promote substrate-induced crack initiations.