X-RAY DIFFRACTION CHARACTERIZATION OF THE RESIDUAL STRESS AND HARDNESS DISTRIBUTIONS IN INDUCTION HARDENED GEARS

Accurate knowledge of the subsurface residual stress and hardness distributions is required for failure analysis, fatigue life prediction and process control of induction hardened components. X-ray diffraction (XRD) provides a powerful tool for the simultaneous determination of both the macroscopic residual stress and hardness distributions through the case and into the core of induction hardened parts. A procedure for developing the empirical relationship between diffraction peak width and mechanical hardness is described. Subsurface XRD residual stress measurement requires layer removal and correction for the resulting stress relaxation. The corrections may dominate the results obtained at depths near the case/core interface. Traditional closed-form corrections may be inadequate when applied to gear teeth. A novel finite element analysis (FEA) correction technique applicable to arbitrary geometries and stress distributions is presented and described. Examples of the determination of the residual stress and hardness distributions through the case of induction hardened gears are presented.