A Practical Estimation of the Residual Stress of Carbonized Spur Gears

Abstract

The residual stress of carburized spur gears is calculated being based on the assumption that the main cause of residual stress is the volume difference between case and core due to the martensitic transformation in cooling. The relation between hardness and carbon content is determined for SCM420H test gears by the measurement, and is used to estimate the specific volumes of the structures from the distribution of hardness. The two-dimensional FEM is used for the calculation The reliability of the method is examined by comparison with stresses measured by the X-ray diffraction method. The present method is then applied to the estimation of residual stress of carburized gears whose hardness and retained austenite are recommended in the AGMA standard. A formula is proposed to estimate the residual stress from hardness and the amount of retained austenite, and it is applied to the estimation of the fatigue strength of carburized spur gear teeth.