The residual stress gradient obtained by the XRD analysis is
presented in figure 7. For the circumferential direction, an
important tensile residual stress at the surface is present. It is
due to an important gradient temperature between two passes
of the cutting edge. For the axial direction, the residual stress
is near zero at the surface of the hole and becomes compressive in depth. Axial and circumferential residual
stresses are insignificant for a depth of 0.25mm.