Investigating the effect of retained austenite on white etching crack behavior of carburized steel under boundary lubrication

 

Sougata Roy1, Benjamin Gould2, Ye Zhou2,3, Nicholaos G. Demas2, Aaron C. Greco2 and Sriram Sundararajan1

 

1Department of Mechanical Engineering, Iowa State University, Ames IA 50011, USA

2Applied Materials Division, Argonne National Laboratory, Argonne IL 60439, USA

3State Key Laboratory of Mechanical Transmissions, Chongqing University, Chongqing 400030, China

Industrial drivetrain components, especially those used in wind-turbine gearboxes experience premature failure due to macropitting or spalling. In many of these cases, the catastrophic failures are caused due to broad branched crack networks surrounded by local regions of nano-grains of microstructurally altered steel known as white etching cracks (WECs). Although the phenomenon of WECs has been reported over a decade, the driving mechanisms are still debated, and the impact of proposed mitigation techniques has not been quantified.  The current study aims to explore the impact of retained austenite (RA) on the formation of WECs within carburized AISI 8620 steel under boundary lubrication. A three ring-on-roller bench top test rig was used to systematically replicate WECs in samples with a wide range of RA. Varying levels of RA had a significant effect on the crack morphology of the failed samples. Under the current test conditions, the microstructural alterations adjacent to the cracks in the lower RA samples were more developed compared to those of the higher RA samples. Additionally, the WEC networks in the high RA samples contained significantly more crack branches than those of the low RA samples.  Potential underlying mechanisms of WEA formation as a function of RA were elucidated. The study helps establish the role of RA on WEC behavior in the context of other mechanical and microstructural phenomena as well as the correlation of rolling contact fatigue behavior to heat treatment routes.