Effect of Loading Mode on Very High Cycle Fatigue Properties of High Speed Steel

Abstract

In order to study the effect of loading mode on fatigue properties of high speed steel (0.7C-4Cr-0.1W-3 Mo-2V) in very high cycle regime, fatigue tests under axial loading and rotating bending condition were performed in laboratory air using the hourglass shaped specimen. From the experiment results, clear duplex S-N curve appeared in both loading conditions, that is, there were two curves composed of a surface failure mode and a subsurface failure mode. Fatigue life under axial loading condition was shorter than that under the rotating bending condition, especially in low stress amplitude level. The difference in fatigue lifetime and transition of failure mode between the loading modes was discussed from the viewpoint of inclusion size, applied stress distribution across the specimen section and residual stress in surface layer.