Microstructural evolution in bearing steel under rolling contact fatigue

The Evolution of White Etching Cracks (WECs) in Rolling Contact Fatigue-Tested 100Cr6 Steel

“…Amorphous-like phases have also been shown to be present in WEA, forming first before WEA is generated [8,14,15]. WEA has been proposed to exist in two ways: deformed WEA consisting predominantly of nanocrystallites and transformed WEA consisting of co-existence between nanocrystallites and amorphous phase [16].…”

“…There is also debate on whether the crack or WEA microstructural change occurs first, whether WEAs form cooperatively with the crack and whether WEA forms gradually or suddenly, where proposed formation mechanisms include amorphisation [8,[14][15][16]35], adiabatic shear, severe localised plastic deformation, low-temperature recrystallisation, carbide break-up and dissolution and electrothermal effects, these being extensively reviewed in [1]. One popular hypothesis is due to crack face rubbing causing a localised mechanical deformation during RCF (this being enhanced in the presence of diffusible hydrogen [36], higher concentrations could exist at these sites [37]), an associated material transfer from one side of the crack to the other occurs, and recrystallisation results [13,37,38].…”

“…The developed crack model quantifies the amount of energy dissipated as a result of friction at crack faces; part of this energy is converted to heat and microstructural decay, WEA formation being a result of amorphisation due to high density dislocation accumulation. The energy generated during crack rubbing leading to amorphisation is also proposed to be sufficient to dissolve large amounts of carbides in the WEA [16]. A counter argument to crack rubbing comes through subsurface inspection using Barkhausen noise measurements, where subsurface changes are investigated without the presence of cracks [39].…”

“…It is suggested that the movement of the crack faces under subsurface shear promoted the formation of WEAs along the crack faces. Finally subsurface crack rubbing has been shown to produce wear debris with an identical composition to the steel matrix, the wear debris being a result of the disintegration of lamellar structure formed during crack rubbing [16].…”

Influence of Slip and Lubrication Regime on the Formation of White Etching Cracks on a Two-Disc Test Rig

“…Some authors propose that the cracks are the precursor of the WEA [4,5], while other authors have suggested that the crack initiation and propagations is a consequence of the formation of WEA [6,7]. Besides a local hydrogen ingress [1] other WEC influence factors such as lubricant composition [1,8], sliding conditions [1,9,10], tensile stresses [1,5] and electrical effects [11] had been proposed.…”