Abstract
In order to investigate the fatigue properties of high strength steels and surface hardened steels in the super-long life range (N≥1×(10)^7), cantilever type rotating bending fatigue tests were carried out for 2 kinds of SNCM 439 steels, which the cleanliness was different on these steels. Also, the surface of notch bottom was removed up to 30μm deep by electro-polishing, because the depth of compression residual stress in the notch bottom of grinding specimen has been 8μm. As a result of fatigue tests, in the case of SNCM 439 (D material) speciem and "high stress amplitude & short life area", it was found that the fatigue life of electro-polishing specimen were almost equal to that of grinding specimen, and in the case of SNCM 439 (S material) speciem and "low stress amplitude & long life area", it was found that the fatigue life of electro-polishing specimen were shorter than that of grinding specimen.
