Abstract
Rotational bending fatigue tests for carbon steel, KSF60 and low alloy steels, KSFA80, KSFA110 were car-ried out to clarify the property of fatigue strength of high tensile forged steels. Fatigue fractures of low alloy steels occurred even though the repeated stress exceeded 108 cycles, which started at interior non-metallic inclusions.
Fatigue strength of the forged material shows anisotropy depending on the relative direction of specimen to forged grain flow, and it is shown that this anisotropy of fatigue strength is due to the projective shape/size of non-metallic inclusions at crack origin to a plain perpendicular to the maximum stress direction. The effect of non-metallic inclusion to fatigue strength was estimated using √area parameter model.
