Abstract
The aim of this work is to characterize the rolling and rolling-sliding contact fatigue failure mechanisms on the 32CrMoV13 nitrided steel. During rolling contact fatigue tests (RCF), two general features were observed: specimens presenting short lives and rough and sharpened spalling damage and specimens presenting long lives and only microspalling marks. It was possible to determine a contact fatigue limit of 3 GPa. During rolling-sliding contact fatigue tests (RSCF), a clearly different behaviour between the two specimens in contact has been observed: the driver shows circumferential and inclined cracks and only inclined cracks appear in the follower. This behaviour can be understood if the effect of the residual stress state in near-surface layers is considered. Before RCF tests, the residual stresses are compressive in all near-surface layers. After RCF tests, strong residual stress relaxation and even reversing behaviour was observed in the axial direction, which facilitates the surface crack initiation in the circumferential direction at rolling track borders.
Highlights
Rolling contact fatigue failure phenomena affect the service life of several different mechanisms and mechanical components, such as, bearings, gears, cams, etc
Concerning the damage mechanisms, surface origin spalling seems to be due to high shear stresses which occur during elastohydrodynamic lubrication, mixed or limit lubrication regimes [11]
Subsurface origin spalling in nitrided steel is generally denominated by “river pattern”, due to its similarity when looked from the top, presenting straight cracks, well-delineated, which appear in the lateral zone of the rolling track [13]
Summary
Rolling contact fatigue failure phenomena affect the service life of several different mechanisms and mechanical components, such as, bearings, gears, cams, etc. Due to “river pattern” spalling shape and the analysis of the spalling’s bottom, some authors suggest that crack nucleation can begin at rolling track edges, spreading out later This spalling morphology of fragile fracture kind was observed in carburized steel with no differences between the spalling kind originated by pure rolling and that originated by rolling-sliding one [14]. This paper intends to contribute to a better knowledge on these phenomena, in the nitrided layers, presenting an experimental characterization of the rolling and rolling-sliding contact fatigue failure mechanisms and the fatigue life of the 32 CrMoV 13 nitrided steel, especially in applications of rolling bearings that are subjected to very high contact stresses. It is intended to study this phenomenon in nitrided layers of bigger depth and carry out a numerical simulation
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