Influence of microstructure and microdefects on long-term fatigue behavior of a Cr–Mo–V steel

Very high cycle fatigue (VHCF) tests at 370 °C were carried out for a Cr–Mo–V steel to investigate the influence of microstructure and microdefects on fatigue behavior. Duplex S–N curves were obtained with the crack initiation switched from specimen surface to interior. A new elliptical type of fish-eye pattern originated from microstructure heterogeneities was observed. In the high cycle fatigue regime, the influence of microstructures on fatigue performance was greater than that of microdefects. In the VHCF regime, by contrast, the fatigue performance was dominated by inclusions and could be interpreted by using the proposed life controlling parameter Z.

► Duplex S–N curves were obtained by push–pull fatigue tests at 370 °C.
► A new elliptical type of fish-eye pattern was observed on fracture surface.
► Microstructure rather than microdefects dominated the HCF behavior.
► Inclusions controlled the VHCF behavior.