EFFECTS OF SURFACE-TREATMENT ON THE BENDING FATIGUE-STRENGTH OF CARBURIZED SPUR GEARS

This paper deals with the effects of surface treatment on the bending fatigue strength of SCM 415 carburized spur gears. The test years are hobbed and carburized, then the tooth surfaces are treated by a combin ation of shot peening, chemical polishing and electropolishing. The re sidual stress is increased by the surface treatment. The SN curves are obtained from the results of a constant stress amplitude fatigue test , and the enhancement of fatigue strength due to the surface treatment is clarified quantitatively. The fatigue strength is well approximate d by an experimental formula which has been proposed to evaluate the s trength from the hardness and residual stress. The effect of variation s in hardness and residual stress of test years is eliminated using th e formula, and the influence of surface roughness on fatigue strength is evaluated. It is approximately equal to the relative surface condit ion factor specified in the ISO strength rating formula.