The characteristics of granular-bright facet in hydrogen pre-charged and uncharged high strength steels in the very high cycle fatigue regime

A review about the effects of structural and operational factors on the gigacycle fatigue of steels

“…When an ODA is observed by SEM with the electron beam being normal to fracture surface, ODA surface is observed as granular. This typical granular morphology is also named fine granular area (FGA) or granular bright facet (GBF) . For simplicity, because ODA, FGA, and GBF named the same typical area on the fracture surface of a specimen tested in the VHCF regime, such area is named FGA hereafter.…”

“…It has been demonstrated that the FGA formation during the very long fatigue process controls the internal fracture mode. FGA is assumed to play a crucial role in the failure mechanism in the VHCF regime . According to Grad and Kerscher, the critical role of internal inclusions in VHCF compared with the role of surface ones is related to a change in the crack propagation rates at the surface compared with the core, especially when the loading is small, close to the threshold of the stress intensity factor range.…”

“…This typical granular morphology is also named fine granular area (FGA) [13][14][15] or granular bright facet (GBF). 9,16,17 For simplicity, because ODA, FGA, and GBF named the same typical area on the fracture surface of a specimen tested in the VHCF regime, such area is named FGA hereafter. It was reported that in the VHCF regime, more than 90% of the fatigue life is attributed to the creation of the FGA.…”

Very high cycle fatigue properties of high‐strength spring steel 60SiCrV7

“…13,14,20 The fatigue strength, fatigue life and the stress intensity factor range at the periphery of GBF (ΔK GBF ) were all decreased for hydrogen-charged highstrength steels with hydrogen content up to 10 ppm. [15][16][17][18][19][20] For example, increasing hydrogen content from 0.6 to 3.0 ppm decreased the fatigue strength at 2 × 10 9 cycles to nearly half of the value of uncharged condition. 20 Although different models concerning the effects of hydrogen on VHCF behaviour of high-strength steels were suggested, the fatigue behaviour and the mechanism of hydrogen influencing fatigue properties in the VHCF regime are still not well understood.…”

“…2 Therefore, the effects of hydrogen on VHCF behaviour have gained much attention. 2,[13][14][15][16][17][18][19][20] It was found that hydrogen trapped by inclusions plays a detrimental effects on the VHCF properties of highstrength steels. 13,14,20 The fatigue strength, fatigue life and the stress intensity factor range at the periphery of GBF (ΔK GBF ) were all decreased for hydrogen-charged highstrength steels with hydrogen content up to 10 ppm.…”