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Abstract The bending fatigue strength of case hardened pulsator test gear wheels has been investigated for wheels in V2158 (20MnCrS5) and fatigue isotropic 158Q (≈ 20NiMo10) steels. The gear wheels in V2158 were forged either vertically or horizontally, the wheels in 158Q just vertically. Structural anisotropy levels were investigated in the horizontally forged V2158 gears. There was no noteworthy level of bending fatigue anisotropy to detect in the V2158 gears. However, the horizontally forged gears performed some 4% better than the vertically forged ones which may be explained by a somewhat more beneficial orientation and dispersion of sulfide inclusions in the horizontal gears. The fatigue isotropic 158Q steel is, in case-hardened components, obviously not required for isotropy reasons but highly appreciated for its outstanding fatigue performance. With identical heat treatment and surface condition, gears in 158Q outperform V2158 gears by some 23% in bending fatigue strength. This is explained by the material's resistance against internal surface oxidation and, to some extend, by its low inclusion content.
Temmel et al. (Wed,) studied this question.