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    Influence of Sulfur Inclusion Content on Rolling Contact Fatigue Life

    Published: 06 October 2014

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    Historically, the performance increase in bearing life has been driven by the increase in material cleanliness. The main focus point for steel manufacturers was improving oxygen content, i.e., reduction to oxygen levels of significantly less than 10 ppm. It was shown that due to this, the lifetime of bearings could be prolonged by orders of magnitude. Here the bearing life could be correlated to the maximum size of oxidic inclusions present in the material. Current results of bearing tests of differently heat treated materials under mixed friction testing conditions have indicated that by minimizing the oxide inclusion sizes, the achievable bearing lifetime could then be dominated by the occurrence of inclusions of ASTM type A, i.e. sulfide inclusions. As this result was rather unexpected and due to the constraints of different heat treatment properties, a systematic evaluation and therefore clear correlation with cleanliness data was not possible. In a more systematic approach, the influence of sulfur inclusion type and size was addressed to identify the effect on bearing performance. To investigate this, different through hardening material heats of 100Cr6 with low oxygen content but significantly differing sulfur contents were chosen. These were evaluated regarding their microscopic cleanliness and angular contact ball bearings were produced. Testing was performed under mixed friction lubrication conditions on angular contact ball bearing test rigs until pitting occurred. Additionally, case hardening materials with differences in sulfur content and therefore maximum sulfur inclusion numbers and sizes were tested under elastohydrodynamic lubrication conditions to study the influence of such inclusions. It was found that the presence of sulfidic inclusions in a shallow depth under the surface leads to surface cracks, but not necessarily to pitting development. However, it was also shown during this test that the majority of bearing failures still can be traced back to nonmetallic inclusions.


    bearing steels, microcleanliness, sulfur, rolling contact fatigue

    Author Information:

    Dinkel, Markus
    Materials Technology Dept., Materials Development Group, Schaeffler Technologies, Schweinfurt,

    Trojahn, Werner
    Materials Technology Dept., Materials Development Group, Schaeffler Technologies, Schweinfurt,

    Committee/Subcommittee: A01.28

    DOI: 10.1520/STP158020140059