Abstract
In order to obtain basic data for high-temperature, high-cycle fatigue properties of S45C(0.45C) and SCM435 (0.35C, 1Cr, 0.15Mo) steels, rotating bending fatigue tests were carried out up to 108 cycles on smooth and two kinds of notch specimens at room temperature, 200, 300, and 500°C with a frequency of 125Hz.
The fatigue strength at 108 cycles and the S-N curves up to 108 cycles were found to change depending upon test temperature and stress concentration factor. The temperature and material dependences of fatigue strength of the smooth specimen were explained qualitatively by the blue brittleness phenomenon of the materials used.
Cracks were observed on the cross section of specimens endured 108 cycles sometimes depending on the test condition. The temperature dependence of the change in fatigue strength due to the variation of stress concentration factor corresponded to the existence of such cracks. The notch root curvature for branch point at 400∼500°C was larger than that at room temperature to 300°C. It is considered that oxidation film formed at the surface of crack plays an important role in delaying for crack to propagate.
