Rolling Contact Fatigue Evaluation of Materials Using the NTN-SNR FB2 Test Rig-A Useful Piece of Equipment for the Qualification of Steels and Steelmakers and for Research

摘要

The NTN-SNR FB2 test rig was developed 40 years ago with the objective to assess the rolling contact fatigue (RCF) life of steels. The aim was to get a relatively quick and cheap evaluation of the performance of steels and processes, on simple rings, under well controlled operating conditions, compared to full scale tests on application rigs. The first part presents the FB2 test rig and the testing conditions used over the years. The use of this test for research and development is then reviewed, through the description of the studies performed to determine the effects of microstructure, fiber flow, deformation ratio, and operating conditions on RCF life, to develop new material solutions, and to understand better failure mechanisms. Attempts to correlate with other RCF tests such as ball to rod or full scale bearing were made with varying degrees of success. The second part presents how the use of this test as part of NTN-SNR steel and steelmakers' qualification procedure has been used profitably as it is able to discriminate between materials of different inclusion cleanliness. The procedure for test conducting and data analysis based on Weibull statistics is described. Twenty years of test results on 100Cr6 are then presented based on a statistical analysis of failure occurrence, and a Weibull analysis of all the results. As the quality of steel has improved over the years, it does not seem suitable to give an L10 result if too few failures occur, and that simple information such as the number of failures and the time to first failure gives a good insight into the steel potential. Other inclusion cleanliness assessment methods are discussed, and compared for EVA (extreme value analysis) with FB2 results. This analysis argues in favour of a combination of FB2 results, technical audit, and inclusion ratings to validate a steel source.