ROLLING-CONTACT FATIGUE RESISTANCE IN AUSROLLED 1-PERCENT C-9310 STEEL

Rolling-contact fatigue is a common failure mechanism for the class of machine elements that includes gears, cams, bearings and sprockets. I mproved endurance through the fabrication of more durable cases in car burized steels was undertaken in the present study, with surface ausfo rming the fabrication technique of interest. Surface ausforming, in a rolling-deformation scheme, was applied to AISI 9310 steel, carburized to 1.0 wt% carbon to a case depth of 1 mm. Ausrolling was applied in two distinct manners, either by a line contact or a point contact die, after quenching the alloy to 235-degrees-C. Ausformed alloy evidenced the lath martensite expected for this thermomechanical processing: it s depth beneath the surface depended on the forming stress, with the p oint contact die inducing the most extensively formed surface. In gene ral, surface hardnesses in ausrolled samples were greater by approxima tely 5.0 HRC than in control samples conventionally marquenched. Rolli ng-contact fatigue endurance for ausrolled microstructures was also su perior to that of conventionally marquenched samples, although subsurf ace oxides introduced during gas carburization degraded the performanc e of the more lightly ausrolled examples. Light surface grinding, whic h removed these artefacts, led to ausrolled surfaces that were over an order of magnitude more durable in rolling-contact fatigue loading th an were those of marquenched-only materials. Ultimately, rolling-conta ct fatigue endurance could be correlated with surface hardness distrib utions for all forms of thermomechanical processing.