Effect of frequency on very high cycle fatigue behavior of a low strength Cr–Ni–Mo–V steel welded joint

• Duplex S–N curve is obtained for the low strength welds at 110 Hz.
• A continuously decreasing S–N curve is seen for the low strength welds at 20 kHz.
• Fine granular area is observed around non-metallic inclusions at 20 kHz.
• Weld metal has more serious frequency effect in the VHCF regime.

Axially fully-reversed fatigue test of a low strength Cr–Ni–Mo–V steel welded joint was conducted up to the very high cycle fatigue regime under the frequency of 110 Hz and 20 kHz. The S–N curve shows a duplex shape at low frequency while decreases continuously at high frequency. Sites of crack initiation and fracture of the welds depend on stress level and loading frequency, hence leading to changed fatigue strength. In addition, frequency effect varies among different parts of the welded joint and fatigue lifetime.