Abstract
The residual stress and microstructure in carburized cases developed by a conventional quench and temper and a hot oil quench were determined for two automotive differential gears. A Ithough the results for the two gears could not be directly compared because of the different geometries, the changes in residual stress produced by hot oil quenching was found to depend on the hardenability of the steels. Hot oil quenched, carburized SAE 4130 drive pinion gears had higher compressive residual stresses than quenched and tempered gears, although the microstructures were similar. The higher compressive stresses are believed caused by 1) the initiation of austenite transformation nearer the core because of the lower thermal gradient, and 2) the elimination of tempering. In contrast, hot oil quenched, carburized SAE 1526 ring gears had lower compressive residual stresses than quenched and tempered gears. The microstructure of the carburized case of quenched and tempered gears was mainly martensitic while bainite was the primary microconstituent in hot oil quenched gears. The lower residual stress in the hot oil quenched ring gears may result from the lower transformation strain associated with the austenite → bainite transformation.
Published Version
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