Fatigue-crack propagation behavior in a high-carbon chromium SUJ2 bearing steel: Role of microstructure

Journal Article · 28 February 2022 · International Journal of Fatigue

DOI: https://doi.org/10.1016/j.ijfatigue.2021.106693 · OSTI ID:1959322

Kowathanakul, Nopasorn ^[1]; Yu, Qin ^[2]; Zhu, Chaoyi ^[3]; Li, Xiaoqing ^[3]; Minor, Andrew M. ^[4]; Ritchie, Robert O. ^[4]

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1. NSK Ltd. Fujisawa (Japan); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
2. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
3. University of California, Berkeley, CA (United States)
4. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); University of California, Berkeley, CA (United States)

High-carbon chromium martensite steels are commonly selected for bearing components in the power generation, automotive and aerospace industries where fatigue failure is a major concern. Accordingly, it is of importance to elucidate the structure-property relationships governing the fatigue properties of such bearing steels. Here, the role of microstructure in influencing the fatigue-crack propagation behavior of a high-carbon chromium SUJ2 bearing steel is examined with emphasis on three martensitic structures: (i) a fine-grained (~10 μm) structure with intragranular (but no intergranular) carbides, (ii) a coarser-grained (~25 μm) structure with discontinuous grain-boundary carbides primarily near triple junctions, and (iii) a coarse-grained (~31 μm) structure with continuous grain-boundary carbides. Although growth rates were fairly similar above ~10^-8 m/cycle, significant differences in behavior were observed at lower, near-threshold growth rates; specifically at a load ratio of 0.1, the ΔKth fatigue threshold was increased from 3.8 MPa m^½ in the fine-grained structure to 5.9 to 6.3 MPa m^½ in the two coarser-grained structures. The dominant factor governing such near-threshold behavior was found to be crack-tip shielding from roughness-induced crack closure, which was most pronounced in the coarser-grained structures; additionally, shielding from crack deflection and branching was apparent in these structures as the crack propagated through the network of intersecting martensite lamellae within the coarse grains. Compared to high-strength stainless steels and low-strength carbon steels, the fine-grained SUJ2 steel displays an exceptional combination of high strength and fatigue-crack growth resistance and is considered to be a superior structural alloy for bearing applications.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: NSK Ltd., Japan; U.S. Office of Naval Research (ONR); USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1959322
• Journal Information: International Journal of Fatigue, Journal Name: International Journal of Fatigue Vol. 156; ISSN 0142-1123
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English