Investigation into microstructural changes due to the rolling contact fatigue of the AISI M50 bearing steel

Abstract

Roller bearings in aircraft turbines are commonly made of AISI M50 steel, because enhanced heat stability as well as highest reliability is required for this application. With a chemical composition of approximately 0.8 C, 4.0 Cr, 4.5 Mo, 1.0 V (all in wt.%) and using a specific vacuum melting and remelting technology for highest cleanliness M50 provides the best properties for such application. Despite some studies on this steel, there is still a lack of information on microstructural evolution during rolling contact fatigue (RCF). Hence, in order to get a better understanding of the microstructural evolution and as a consequence of the crack initiation, in the framework of this study a comprehensive set of experimental techniques were combined. For the RCF loading a so called ball-on-rod test was used. Microstructural alterations were analysed by various methods including optical light microscopy, confocal microscopy, scanning electron microscopy (SEM) with cross-sectional cutting by focussed ion beam (FIB), transmission electron microscopy (TEM) and microhardness measurements. Testing methods showed the build-up of a so-called white etching area (WEA) in a certain region below the raceway and the formation of butterfly-wings (BW) with micro-cracks at local microstructural inhomogeneity. Furthermore, all tested samples showed BW's which initiated on carbides, often with micro-cracks near the boundary to the matrix.

Feasability Investigation for Laser Powder Bed Fusion of High-Speed Steel AISI M50 with Base Preheating System

“…This paper focuses on the high-speed steel (bearing steel) AISI M50, also known as 1.3551 or 80MoCrV42-16, with 0.8 wt.-% carbon content. M50 is used in the rolling bearing industry in conventional production as a standard material [14]. It is a suitable alloy for rolling bearings due to the high initial hardness after martensitic hardening and high-temperature strength.…”

Crack path and regularities for ball‐bearing fracture in the very‐high‐cycle fatigue regime

“…The described observations allowed to make an assumption that the similar "butterflies" and cracks in the region of "butterfly wings" might be an origin for subsurface crack resulting in the fatigue spalling. 27 However, it was not emphasized that the presented results indicate the realization of the stress state belonging to the VHCF regime.…”

“…After reaching durability of 10 8 overrollings, the “butterfly wings” below the layer of the WEA were identified with a cluster of carbides in the middle of the “butterfly.” Instead of the martensite structure of the material in its initial state, the nanocrystalline structure inside the region of “butterfly wings” was established by transmission electron microscopy and the rings on diffraction patterns. The described observations allowed to make an assumption that the similar “butterflies” and cracks in the region of “butterfly wings” might be an origin for subsurface crack resulting in the fatigue spalling 27 . However, it was not emphasized that the presented results indicate the realization of the stress state belonging to the VHCF regime.…”

“…The fatigue spalling process with the formation of subsurface WEA layer and "butterfly wings" beneath this layer was investigated by using a ball-on-rod testing machine. 27 The cylindrical specimens of AISI M50 steel are rotated and loaded with three balls resulting in a realization of maximum Hertzian contact stress of 6.4 GPa which is approximately three times higher than the highest operational load in aircraft turbines during take-off. The microstructural evolution during rolling contact fatigue was analyzed at the number of overrollings from 10 4 to 1.9 Â 10 8 .…”

Crack path and regularities for ball-bearing fracture in the very high cycle fatigue regime

“…The fatigue spalling process with the formation of subsurface WEA layer and "butterfly wings" beneath this layer was investigated by using a ball-on-rod testing machine. 27 The cylindrical specimens of AISI M50 steel are rotated and loaded with three balls resulting in a realization of maximum Hertzian contact stress of 6.4 GPa which is approximately three times higher than the highest operational load in aircraft turbines during take-off. The microstructural evolution during rolling contact fatigue was analyzed at the number of overrollings from 10 4 to 1,9×10 8 .…”