## 1 Introduction  
Rolling contact fatigue failure phenomena affect the service life of several different mechanisms and mechanical components, such as, bearings, gears, cams, etc. These kinds of fatigue failure phenomena are usually divided in two main mechanisms: microcrack nucleation and crack propagation [1]. Several damage mechanisms related to the failure of lubricated hertzian contacts have been identified [2; 3; 4; 5; 6; 7; 8; 9]. [PERSON] [10] proposed two deterioration levels (spalling and surface distress) and three kinds of damage mechanisms (surface origin spalling, microspalling or micropitting and subsurface origin spalling). 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]. Their in-depth propagation occurs due to microspalling coalescence, implying high enough tensile loadings to originate stress concentration at cracks tips and lubricant action [10]. Microspalling often arises from the grinding grooves, being the dimensions of this kind of damage of about 7 to 10 \(\upmu\)m at the near surface and between 10 to 50 \(\upmu\)m in depth. These dimensions can seem very small, but it should be noted that microspalling can grow through the whole contact track, leading to disturbances of the contact condition, originating large spalling and, finally, leading to a complete rupture of the structure [1; 12]. On the rolling-sliding conditions, the damaged surface presents V shape microspalling and cross cracks at the track's surface. Cracks presenting an inclination angle to the surface of 20-30 degrees have been observed. 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]. Crack nucleation begins at a certain depth, leading to spalling occurrence by axial and circumferential propagation. On the other hand, 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 also observed in carburized steel with no differences between the spalling kind originated by pure rolling and that originated by rolling-sliding one [14]. Continuous demands for better material performance, in applications with highly stressed surface layers due to high contact and fatigue loading, imply development of new materials, new processes and new treatments to be applied to these surface layers [15; 16; 17; 18; 19]. New coating materials or surface treatments can be applied to bulk materials to improve the strength of their near surface layers. In the case of steel components, the recent processes and treatments allow us to obtain steels with high purity and without inclusions, implying a better knowledge of the nucleation processes on the role of the fatigue contact phenomena [20]. The trend in recent years has been to research and apply treatments and techniques to the surface layers, that create high compressive residual stresses and gradients of mechanical properties to obtain a high mechanical strength in the zones more requested, keeping the traditional properties of the bulk materials unchanged. The nitride steel studied in this work exhibits important properties in terms of hardness, hot hardness, high toughness, contact fatigue life, wear, and corrosion endurance. These characteristics make it particularly suitable for severe application conditions, namely, aeronautic bearings [21; 22], helicopter transmission gears [23], manufacturing specific parts submitted to important efforts [24] and applications to wood machining [25; 26]. An experimental and numerical rolling contact study on this quenching and tempered 32 CrMoV 13 steel was made [27].