X-Ray Diffraction Characterization of Residual Stress and Hardness Distribution 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.