Shot peened VDSiCr spring steel has been investigated under cyclic torsional and axial loading at load ratios between R=-1 and R=0.5. The ultrasonic fatigue testing method is used to collect fatigue data in the range between 105 and 1010 cycles. Mean stress sensitivities and VHCF strengths are compared for both loading conditions. Damage mechanisms leading to failures in the VHCF regime are different for axial and torsional loading. Inclusions and fractured grain boundaries are preferential crack initiation sites under cyclic axial loading. VHCF cracks produced by cyclic torsion loading are mainly initiated internally by cyclic shear without the presence of a material inhomogeneity. The initial mode II / mode III cracks change their paths to mode I at a well defined stress intensity. Residual stresses are affected by cyclic torsion but not by axial VHCF loading.
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