Bearing Fatigue Life: The Detrimental Effect of Carbide Segregation

摘要

It has been well established that carbide segregation is extremely detrimental to the rolling contact fatigue (RCF) life of bearings. It has been estimated that the rolling element fatigue resistance can decrease by as much as a factor of four due to carbide segregation. RCF testing was performed on two different sources of 6310 bearings to compare the results of a top tier bearing supplier to a lower cost alternative. The calculated L_(10) life of the bearings from the top tier supplier was over 28 times that of the alternative source. This launched an investigation into the root cause of the dramatic reduction in bearing life.Initial comparisons between the two manufacturers did not reveal the root cause. Both brands appeared similar with regards to dimensional tolerances, 52100 chemistry and hardness typical of a through hardened microstructure. However, once a thorough investigation was performed on the failure mechanism and microstructure of the alternative brand, it became apparent that the alternative brand exhibited a high degree of carbide segregation. The heavy carbide bands present within the material created regionally hard and soft areas, thus creating discontinuity within the microstructure which led to micro-cracking and premature failure. Superior steel quality with a homogenous microstructure is imperative to extending the RCF life in all bearings. This provides a matrix of finely dispersed spheroidal carbides that impart maximum material strength and toughness to the steel which ultimately extends the fatigue life of the bearing.