Period of Fine Granular Area Formation of Bearing Steel in Very High Cycle Fatigue Regime

Abstract:

In order to examine the period of fine granular area (FGA) formation of bearing steel in very high cycle fatigue regime, rotating bending fatigue tests were carried out at the stress amplitude 1100 MPa below the fatigue limit. The tests were interrupted at the cumulative damage values ranging from 0.1 to 0.5 with an increment of 0.1 to charge hydrogen to the specimens. After the charge, the rotating bending tests were continuously carried out. The crack origin areas on all fracture surfaces were checked by a scanning electron microscope (SEM), and it was discovered that FGA was not formed in some of them. From a view point of fracture mechanics, the stress intensity factor ranges of FGA areas, ΔK_FGA, were calculated by using Murakamis area model. The ΔK_FGA values increase with the increase of the cumulative damage values. Furthermore, ΔK_FGA values in this study were smaller than 5 MPam which was obtained from usual fatigue testing. Therefore, we conclude that the stable crack growth stage starts when the threshold stress intensity factor range decreases due to hydrogen embrittlement in the middle of formation of FGA.

• Periodical: Advanced Materials Research (Volumes 891-892)
• Pages: 434-439
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.891-892.434
• Online since: March 2014
• Authors: Noriyasu Oguma*, Naoya Sekisugi, Katsuyuki Kida, Yasuhiro Odake, Tatsuo Sakai
• Keywords: Bearing Steel, Fine Granular Area, Rotating Bending, Very High Cycle Fatigue (VHCF)

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