Effects of natural aging and variable loading on very high cycle fatigue behavior of a bearing steel GCr15

Abstract

Natural aging and variable amplitude loading are very common for structural parts subjected to fatigue loading. In this paper, ultrasonic frequency fatigue tests without intermittence were conducted to investigate the effects of natural aging and variable amplitude loading on very high cycle fatigue (VHCF) behavior of a high strength steel GCr15. It was shown that a natural aging of 10000 h prolonged the fatigue life of GCr15 steel in VHCF regime. The reason was that more granular carbides precipitated in the microstructure after the natural aging, and they strengthened the fatigue resistance of the material. The natural aging had no influence on the characteristics of the crack initiation and early growth region of GCr15 steel in VHCF regime. The effect of low loading in variable amplitude on fatigue life was related to its loading sequence, loading cycles and stress level. Under step loadings, the low loading with a number of cycles could reduce the fatigue life. The high loading in variable amplitude with a small number of cycles accelerated the crack initiation and growth. It could also change the fatigue failure mechanism to the one dominated by high loading.