Abstract
This paper deals with the effects of surface treatment on the bending fatigue strength of SCM 415 carburized spur gears. The test gears are hobbed and carburized, then the tooth surfaces are treated by a combination of shot peening, chemical polishing and electropolishing. The residual 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 approximated by an experimental formula which has been proposed to evaluate the strength from the hardness and residual stress. The effect of variations in hardness and residual stress of test gears is eliminated using the formula, and the influence of surface roughness on fatigue strength is evaluated. It is approximately equal to the relative surface condition factor specified in the ISO strength rating formula.
