Increase in Fatigue Limit of Gears by Compound Surface Refining Using Vacuum Carburizing, Contour Induction Hardening and Double Shot Peening

To increase the fatigue limit of the Carburized gears, the following five techniques need to be developed: 1) Reduce abnormal surface structure. 2) Obtain a fine grain size. 3) Decrease the retained Austenite structure. 4) Increase hardness under the surface. 5) Improve the residual stress distribution under the surface. For this purpose, the authors conducted a study by using DSG1 steel gears on the new compound surface refining method consisting of Vacuum Carburizing, Contour Induction Hardening and Double Shot Peening. The result of the study showed that the fatigue limit of the gears processed by the new compound surface refining method achieved 150% better than that of the single processed Vacuum Carburized gears. Furthermore, the authors analyzed the correlation between the fatigue limit and the yield stress, the maximum compressive residual stress & the mean grain size of gears systematically, the consequence of which was the fatigue limit given with an equation.