WIT Press


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

Price

Free (open access)

Paper DOI

10.2495/SECM150041

Volume

91

Pages

11

Page Range

35 - 45

Published

2015

Size

1,353 kb

Author(s)

L. Pritz, S. Marsoner, R. Ebner, R. Fluch, A. Tatschl, R. Münzer

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.

Keywords

bearing steel, M50, RCF, rolling contact fatigue, fatigue crack initiation, WEA, butterfly wings