THE INFLUENCE OF HIGH CONTACT STRESSES AND LUBRICANT TYPE ON THE ROLLING CONTACT FATIGUE LIFE AND FAILURE MODE OF AISI 52100 STEEL BALLS

This paper presents an experimental investigation to evaluate the rolling contact fatigue (RCF) performance and failure mode of AISI 52100 steel balls under conditions of high contact stresses and three different types of lubricating oils using rolling four-ball tester. The values of high contact stresses were varied between 6.74 GPa and 8.89 GPa. The lubricants tested were PG220 synthetic oil, mineral oil, and grease. Test results revealed that: 1) for all the used lubrication oils, the contact stress of 7.28 GPa represents a threshold value after which RCF life of tested steel balls was very short; 2) for the same contact stress, the film thickness with a PG220 synthetic oil is 65% and 10% thicker than that with a mineral oil and grease, respectively. This makes the steel balls life with PG220 synthetic oil approximately seven times and five times greater than that with a mineral oil and grease, respectively. Post-test surfaces and failures were examined using light microscopy. It was found that at different values of high contact stress, subsurface-initiated fatigue spalling is the main mode of RCF failure with PG220 synthetic oil and grease, while surface-initiated fatigue spalling mode of RCF failure prevails with a mineral oil.