Scuffing characteristics of SAE 50B38 steel under lubricated conditions

The scuffing characteristics of SAE 5OB38 steel were investigated under lubricated conditions using a block-on-ring bench tester. The main purpose of this study was to better understand the failure mechanism(s) of lubricated steel contacts operating under boundary lubrication conditions. Scuffing tests were conducted with a polyalphaolefin (PAO) lubricant at various sliding speeds. A scuffing transition map, which is characterized by three regions (mild wear, microscuffing and catastrophic scuffing failure), was developed over ranges of applied load and sliding speed. To better understand the scuffing processes and failure mechanisms, the tests were interrupted during the scuffing process. The surfaces and subsurfaces of specimens obtained at various stages of scuffing were examined with SEM (scanning electron microscope), TEM (transmission electron microscope) and a nano-indentor. Based on the experimental observations, it is hypothesized that scuffing failure is caused by macroscopic adhesion at the sliding interface, which eventually leads to the plastic shearing of bulk, material. It was also found that the scuffed subsurface of SAE 50B38 steel exhibits three characteristic regions (transformed layer, plastically deformed layer and bulk material). The transformed layer has a nanocrystalline structure, indicating the microstructural change during scuffing failure.