Investigation Into Microstructural Changes Due To The Rolling Contact Fatigue Of The AISI M50 Bearing Steel

• Published in: WIT Transactions on Engineering Sciences Vol. 91; p. 35
• Main Authors: Pritz, L, Marsoner, S, Ebner, R, Fluch, R, Tatschl, A, Münzer, R
• Format: Journal Article
• Language: English
• Published: Southampton W I T Press 01.01.2015
• Subjects: Bearing steels; Chemical composition; Chromium; Crack initiation; Evolution; Fatigue cracks; Fracture mechanics; High speed tool steels; Inhomogeneity; Ion beams; Measurement methods; Melting; Metal fatigue; Microcracks; Microhardness; Microscopy; Molybdenum; Organic chemistry; Roller bearings; Rolling contact; Scanning electron microscopy; Test procedures; Transmission electron microscopy; Turbines; Vacuum melting; Wings (aircraft)
• ISSN: 1746-4471; 1743-3533
• DOI: 10.2495/SECM150041

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.