Influence of Modified Oxide Inclusions on Initiation of Rolling Contact Fatigue Cracks in Bearing Steel

In order to elucidate the mechanism by which the modification of oxide inclusions in bearing steel leads to the improvement of rolling contact fatigue (RCF) properties, a study was conducted with particular attention to the difference in the crack initiation time. Compared with normal Al-killed steel, non-Al-killed steel with modified oxide inclusions has been confirmed to exhibit improved rolling contact fatigue properties. Investigations using ultrasonic testing (UT) and acoustic emission (AE) have revealed that the non-Al-killed steel has a smaller number of defects detected by UT and the number of signals detected by AE, both indicating the suppressed initiation of initial cracks. A study done on the reasons shows that SiO2-based inclusions generated in the non-Al-killed steel have excellent adhesion between each inclusion and the matrix, with a smaller difference in Young's modulus between them. Therefore, it is conceivable that the non-Al-killed steel experiences a decreased amount of the strain change that occurs in the vicinity of inclusions during rolling load, which suppresses the initiation of initial cracks and improves the rolling contact fatigue properties.