Retained austenite stability on rolling contact fatigue performance of 8620 case‐carburized steel

Abstract

Varying levels of retained austenite (RA) were achieved through varying undercooling severity in uniformly treated case carburized 8620 steel. Specimens were characterized via XRD and EBSD techniques to determine RA volume fraction and material characteristics prior to rolling contact fatigue (RCF). Higher RA volume fractions did not lead to improvement in RCF lives.XRD measurements after RCF testing indicated that little RA decomposition had occurred during RCF. A continuum damage mechanics (CDM) finite element model (FEM) was then developed to investigate the effects of RA stability on RCF. The results obtained from the CDM FEM captured similar behavior observed in the experimental results. Utilizing the CDM FEM, a parametric study was undertaken to examine the effects of RA quantity, RA stability, and applied pressure on RCF performance. The study demonstrates that the energy requirements to transform the RA phase are critical to RCF performance.

Observation of flaking process in rolling contact fatigue of bearing steel with spheroidal inclusions by laminography using ultrabright synchrotron radiation X‐rays

“…As the number of fatigue cycles increases, characteristic microstructures appear, such as the white band (WB), 15,16 which is type a of shear band, the white etching band (WEB), 15,17 white etching area (WEA), 15,18–24 white etching cracks (WECs), 17,19 brown etching layer (BEL), 18 and butterfly cracks 20 . The WEA was found to be composed of ultrafine nanocrystalline ferrite grains, voids, and spherical carbides, as observed by transmission electron microscopy 19–23 . Hiraoka et al 5 observed that WEA occurred after microcrack initiation.…”

“…In RCF, microstructural alternation of the matrix under the surface is an important cause of RCF without friction under oil lubrication. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Such alterations may be a dark etching area (DEA), 15,16 dark etching constituent (DEC), 15 dark etching region (DER), 15,17 and martensite transformation from retained austenite, 16,21 which occur in high-stress regions under the raceway. As the number of fatigue cycles increases, characteristic microstructures appear, such as the white band (WB), 15,16 which is type a of shear band, the white etching band (WEB), 15,17 white etching area (WEA), 15,[18][19][20][21][22][23][24] white etching cracks (WECs), 17,19 brown etching layer (BEL), 18 and butterfly cracks.…”

“…[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Such alterations may be a dark etching area (DEA), 15,16 dark etching constituent (DEC), 15 dark etching region (DER), 15,17 and martensite transformation from retained austenite, 16,21 which occur in high-stress regions under the raceway. As the number of fatigue cycles increases, characteristic microstructures appear, such as the white band (WB), 15,16 which is type a of shear band, the white etching band (WEB), 15,17 white etching area (WEA), 15,[18][19][20][21][22][23][24] white etching cracks (WECs), 17,19 brown etching layer (BEL), 18 and butterfly cracks. 20 The WEA was found to be composed of ultrafine nanocrystalline ferrite grains, voids, and spherical carbides, as observed by transmission electron microscopy.…”

“…20 The WEA was found to be composed of ultrafine nanocrystalline ferrite grains, voids, and spherical carbides, as observed by transmission electron microscopy. [19][20][21][22][23] Hiraoka et al 5 observed that WEA occurred after microcrack initiation. Martin et al 25 examined microstructural alterations, which develop with cyclic stressing under rolling contact, and attempted to define their nature and formation mechanisms.…”

“…In RCF, microstructural alternation of the matrix under the surface is an important cause of RCF without friction under oil lubrication 11–27 . Such alterations may be a dark etching area (DEA), 15,16 dark etching constituent (DEC), 15 dark etching region (DER), 15,17 and martensite transformation from retained austenite, 16,21 which occur in high‐stress regions under the raceway.…”