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    STP1600

    Improvement of Fatigue Life Caused by Surface-Initiated Flaking in Rolling and Sliding Contact Condition by Modification of Subsurface Microstructure

    Published: 11 December 2017


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    Abstract

    The most common failure in bearings under well-controlled lubricating conditions is internal-originated flaking. In contrast, surface-originated flaking, such as pitting, occurs in bearings and gears under rolling contact fatigue (RCF) with sliding contact. The friction force between steel parts in sliding contact causes surface damage. As a result, the parts’ flaking initiation is changed from the inside to the surface. Nowadays, due to the two following changes in global environmental issues, steel parts are expected to endure more serious conditions. (1) To suit the needs for reduction in size and weight, the allowable stress of steel parts tends to increase. (2) To improve power-transmission efficiency, viscosity of lubricant oil tends to decrease. In order to respond to these changes, clarification of the flaking mechanism is very important. However, under RCF with sliding contact, surface conditions such as texture and roughness change from moment to moment. These changes make it difficult to clarify the mechanism of surface-originated flaking. In the present work, the influence of subsurface microstructure of carburized steel on surface-originated flaking life was investigated under RCF with sliding contact. Chemical compositions of steel were varied to transform the subsurface microstructure after gas carburizing. Surface-originated flaking life was changed depending on the subsurface microstructure, which consists of intergranular oxide and incomplete quenching structure. Some RCF tests were interrupted and the wear of raceway and cross-sectional microstructure around the surface cracks was observed. The results indicated that the surface-originated flaking life can be improved by suppression of harmful surface cracks originating from intergranular oxides.

    Keywords:

    pitting life, rolling contact fatigue (RCF), intergranular oxidation, abnormal carburized layer, gas carburized, high silicon (Si) and chromium (Cr) steel


    Author Information:

    Maruyama, Takashi
    Sanyo Special Steel Co., LTD, Research & Development Center, Hyogo,

    Fujimatsu, Takeshi
    Sanyo Special Steel Co., LTD, Research & Development Center, Hyogo,

    Tsunekage, Norimasa
    Sanyo Special Steel Co., LTD, Research & Development Center, Hyogo,


    Committee/Subcommittee: A01.28

    DOI: 10.1520/STP160020170021