This study investigates and compares the evolution of subsurface hardness and microstructure of Hybrid 60 and 52100 steels under rolling contact fatigue (RCF) testing. Similar microstructural decay was identified for both Hybrid 60 and 52100 steel, evidenced by the formation of elongated ferrite and ferrite microbands during the first stage of the microstructural decay. Nano-sized ferrite grains were also observed in the region with maximum Hertzian stress after 1×108 stress cycles for both steels. In addition to the common microstructural decay in the two steels, the 52100 steel experienced microstructural decay in the form of dissolution of residual cementite and tempered carbides. The present study shows that the Hybrid 60 steel develops less microstructural decay than the 52100 steel at the same RCF conditions suggesting that Hybrid 60 could be suitable for replacing 52100 in applications where higher RCF is needed. The improved microstructure stability in Hybrid 60 is attributed to the more stable secondary carbides and intermetallic precipitates as compared to the cementite in the 52100 steel.

Material decay in bearing steels under rolling contact fatigue (RCF) leads to fatigue initiation and failure. This study examines the local structure-property relationship in decayed material through in-situ compression testing of micropillars prepared from a dual-hardening martensitic bearing steel (Hybrid 60) before and after RCF testing. The results demonstrate a pronounced enhancement in local yield strength for decayed regions (2200–2340 MPa) as compared to non-decayed regions (1755–1780 MPa). The higher initial stress for dislocations glide in the decayed regions and their discontinuous yield behavior are attributed to the presence of ferrite microbands. Crystal plasticity simulations corroborated these findings, showingincreased critical resolved shear stress (CRSS) and reduced strain hardening in decayed samples.

We investigate the microstructural degradation during rolling contact fatigue (RCF) in a martensitic dual-hardening bearing steel. The dual-hardening steel makes use of both carbide precipitation and intermetallic precipitation hardening. The microstructural degradation leading to fatigue failure is studied using electron microscopy, atom probe tomography, and synchrotron X-ray diffraction (SXRD). The initial microstructure of the steel consists of tempered martensite with a fine dispersion of secondary M7C3, and NiAl precipitates. During RCF testing at 2.2 GPa contact pressure, ferrite microbands develop and the partial dissolution of NiAl and M7C3 precipitates occur within the ferrite microbands. For the RCF testing at higher contact pressure of 2.8 GPa, nanosized ferrite grains develop in the ferrite microbands. The SXRD analysis reveals a decrease in dislocation density in the sub-surface region experiencing microstructural degradation. This is believed to be associated with the rearrangement of dislocations into low energy configuration cells. We conclude this manuscript by proposing a microstructure decay mechanism for martensitic dual-hardening bearing steel that provides insights in the fatigue initiation process.

This comparative study investigates the microstructure decay in one martensiticlow-carbon steel (Hardox 400), and one precipitation-strengthened martensitic low carbon steel (Hybrid 60) during cyclic contact loading. The primary objective isto directly compare the resistance to material decay for martensitic steel with andwithout precipitation-strengthening. The microstructural decay is characterized indetail using scanning electron microscopy, electron backscatter diffraction, and atom probe tomography. It is found that both steels have similar microstructural decay, including the formation of ferrite microbands and nano ferrite grains. However,  the Hybrid 60 steel demonstrates superior microstructure stability due to the effectiveness of its precipitates in inhibiting cyclic plastic deformation. The NiAl and M7C3 precipitates have a high resistance to dissolution and their ability to immobilize dislocations, impedes the material degradation, and could prolong service life in contact fatigue applications. 

Subsurface rolling contact fatigue (RCF) failure occurs beneath heavily loaded hard contacts like gears, bearings, and cams. This study investigates microstructural decay beneath a RCF-tested surface in AISI/SAE 52100 bearing steel tempered at 240 ℃. RCF tests were conducted at 100 ℃ with a maximum Hertzian contact pressure of 4 GPa for four stress cycles. Microstructural characterization utilized scanning electron microscopy, electron backscatter diffraction, transmission Kikuchi diffraction, and transmission electron microscopy. Due to high tempering temperature, white etching bands (WEBs) were observed without preceding dark etching regions. The microstructural decay sequence involved: (1) formation of elongated ferrite and ferrite microbands, (2) complete dissolution of tempered carbides and partial dissolution of residual cementite, (3) formation of WEBs composed of nano-sized ferrite grains (100–300 nm) transformed from ferrite microbands, and (4) appearance of lenticular carbides. Within the WEBs, most nano-sized grains had high-angle grain boundaries, while the fraction of low-angle grain boundaries increased in later stages of RCF. Lenticular carbides formed alongside elongated ferrite and coalesced nano-sized ferritic grains.

We investigate the microstructural degradation during rolling contact fatigue (RCF) in a novel martensitic dual-hardening steel. The microstructural decay that eventually leads to fatigue failure is studied by electron microscopy, atom probe tomography and synchrotron X-ray diffraction (SXRD). The initial microstructure of the steelconsists of tempered martensite with a fine dispersion of secondary M7C3, and NiAl precipitates. During RCF testing at 2.2 GPa contact pressure, ferrite microbands develop and the partial dissolution of NiAl and M7C3 precipitates occur within theferrite microbands. For the RCF testing at higher contact pressure of 2.8 GPa, nanosized ferrite grains develop in the ferrite microbands. The SXRD analysis reveals a decrease in dislocation density in the sub-surface region experiencing microstructural decay. This is believed to be associated with the rearrangement of dislocations into low energy configuration cells. We conclude this manuscript by proposing a microstructure decay mechanism for dual-hardening martensitic steels that provides insights in the fatigue initiation process.

Material decay in bearing steels under rolling contact fatigue (RCF) leads to fatigue initiation and failure. This study examines the local structure-property relationshipin decayed material through in-situ compression testing of micropillars prepared froma dual-hardening martensitic bearing steel (Hybrid 60) before and after RCF testing. Specific crystal orientations are tested, revealing differing plastic behavior in the virgin and decayed material. RCF-induced ferritic microbands create highly localized deformation, that alters the micromechanical response. Crystal plasticity simulations confirm these findings, highlighting increased critical resolved shear stress and reduced strain hardening in decayed micropillars.